Chloe issues (random aggression)

Since summer started, I have not been around the house much, so almost all of these incidents I am being made aware of after the fact. But I honestly don't know what to do. I am going to be purchasing a muzzle asap (anybody recommend a good brand?), but if anyone has any advice for behavior modification work that would be wonderful.

The backstory for those of you that don't know her well: Chloe is a five year old spayed Aussie/farm collie mix. I adopted around nine weeks old; prior she was living in a barn with zero outside world exposure. I know other litter mates of hers and they all have a similar anxious disposition, but Chloe also has aggression issues. When she was a pup she had no tolerance for being handled/restrained, had severe resource aggression, reactivity towards other dogs, I couldn't groom her without her seriously biting, etc., etc. Most of those issues have been worked through now. She went through a phase of serious place guarding for awhile, but that diminished to just not liking being messed with when she was laying down and sleeping which is easy to avoid.

Recent issues:

Over Christmas she bit my brother in the face. She was greeting him and he started roughing up on her like he does his roommates dogs and he wrapped her in a hug - she bit him in the face and left two puncture wounds. Typically if someone is stupid enough to restrain her she is either okay with it or will just growl/air snap, so the physical contact was new.

We've had an incident or two in the past few months of her growling at people when they bump in to her while she is on the sofa resting. She does the same thing when she is just laying down resting, so I assumed it was the same issue, just in a different place. New rule was that Chloe was not allowed on the furniture when guests were present just in case.

It appears now she is escalating.

In the past two weeks she has attacked three visitors. Now, "attack" is subjective. She has growled/snarled/snapped/lunged at three visitors - she made contact with one, didn't break skin (left two red marks on her face). All "attacks" were sudden and without warning (knowing Chloe, she probably tensed and got hard eyed a split second before). All "attacks" were also brief and probably only lasted literally a second. Kind of like when you're trimming a dog's nails and he screams and whips around at you - he doesn't continue to assault you when you GTF out of the way.

First instance: My grandparents were up visiting over Memorial Day. As they were leaving, Chloe was laying down in the entry way. Grandpa reached down to pet her and she snarled and lunged for his face. No contact was made.

Second instance: On of my sister's friends was sitting on the couch, watching a movie or something. Chloe was on the floor. Chloe lunged after the friend for no apparent reason. Again, no contact was made.

Last night Mike, Sam, and I all went out to the house and were shooting guns most of the afternoon. When we had packed up I was letting Chloe run around in the yard on her drag line with us and she was playing with the other three dogs and having a good ol' time. I didn't notice any abnormal behavior on her part. She was interacting really well with everybody, including Sam who she had only met once before. Mike had a headache and wasn't feeling well, so we left early and I put Chloe up in the house so my family didn't have to keep an eye on her outside.
Later, my brother and his girlfriend showed up for the cookout. Chloe was excited to see them and went up to greet them. Bre was just petting her (no bear hugging involved) and Chloe lunged up and bit her in the face. Contact was made, no puncture wounds, just two red marks on her cheeks.

This is unacceptable. She is fine 99% of the time, but for the love of God I cannot figure out what is going through her brain when she is aggressing at people. These are people she would normally not have an issue with in situations she would normally be okay in.

I absolutely cannot trust her anymore and I don't know what to do. She will now either be kept in my room when visitors are over or she will be muzzled, end of story. She absolutely HATES being kept penned up away from everybody, so I think the muzzle scenario is going to be more likely as she'll turn into an anxious mess otherwise. But I am worried she is going to keep escalating and one day someone will screw up and she is going to seriously bite someone. I do not want that happening.

And although Mike and I won't be living together for another year, when I move out in August she is going to start being around him almost all the time and he is going to be helping me out with potty breaks and such for her. Although she has never shown any issue towards him at all, he's not me or my sister and we are the only two people she has ever not aggressed randomly towards. I'm worried that Mike's going to trigger her in some way, especially since he is used to his dogs that let him do anything to them, and she is going to bite him.
She's put her teeth on him once before (he went to pet her, I think, while she was resting - I was upstairs and not around), but he wasn't concerned about it because she didn't do anything to him. However, if she's escalating, the next time it will be a bite and Mike's initial response is going to be a Come to Jesus meeting....which is not an effective method with Chloe, me having done so before.

My sister and I had talked briefly about me actually giving her Chloe (she takes care of her when I'm gone and Chloe is just as bonded to my sister as she is to me, if not more so), but I don't know if that is such a good idea now. JeanAnne is responsible with her and would manage her properly, but I don't think it would be fair or wise to have a 17 year old be the sole owner of an aggressive dog. But, then again, Chloe would also be kept in the environment she grew up in with people she knows and who know her, which might be beneficial versus moving into an apartment with me and suddenly being in a new, small area and constantly being on the go, adapting to three other dogs and a new second "owner", with other moves in the near future being a high probability.

Gah, I just don't know. Thoughts, comments, advice, behavioral modification plan ideas? I love this dog and she is brilliant when she's around my sister or I, but she is making it very difficult to own her right now.

First, is there any chance she is loosing her hearing or eye sight? Any chance there is pain? I think a vet visit is in order, it seems like a very sudden change and a medical cause sounds probable.

I definitely think a muzzle is a good idea until you can get a good handle on what exactly is causing this. Aggression without an easy to define trigger is always going to be difficult to deal with, it's hard to say whether or not you've made improvements unless you know what situations would normally cause aggression. To start I would just put in daily effort to work on her handling issues. Lots of counter conditioning to touching her everywhere. I'd also work on getting her used to being touched while resting if this can be done safely, again counter condition it. Gentle touch, treat, then work up to harder touches, bumping her with your hip, etc. for treats. Have other family members (Adults) work on it too if that's safe.

But management will be very important I think. Use the muzzle and tell people right off the bat to leave her alone, especially if she's lying down.

If the vet visit doesn't turn anything up you might want a behaviorist to come help you try and figure out a plan.

iirc you're very close to Purdue - now might be the time to consider getting an appointment with their vet behaviorist team at the Animal Behavior Clinic.

Nope, no loss of eyesight or hearing. She's also physically fine. She has a bum back leg that she gets touchy towards if you manipulate it or hit it while playing with her, but it isn't anything extreme. That mainly causes her to be grumpy with other dogs that try to play rough with her - I think the only time she's ever acted out towards a person because of it is during grooming when we pick the leg up. A few years ago she would snap at people petting her on the head due to an ear infection she had, but her ears are good. When she was about two, I think (whenever she was having the serious space guarding issues that seemed to just pop out of nowhere), I had her thyroid checked and all that fun stuff and everything was normal.

I've been working on counter conditioning all her life and we've made vast improvements, but I feel like we've hit a wall. I personally can do anything I want to her and she's fine, but she doesn't generalize well. She does to a point, but not enough for the work I have personally done with her to matter too much when it comes to strangers.
For example, I can groom her head to toe without any issues from her at all. The groomer, on the other hand, can only do so much without Chloe getting pissy and I either have to hold her or she has to be muzzled. (Which is why I learned how to do it myself.) Because of the work I've done with her she tolerates much more and behaves much better than what she used to, but I'd still say she's only about 75-80% reliable with other people she's somewhat used to and about 97% reliable with family members.

I also can't really afford a behaviorist session at Purdue. $350 for the first session, $100 for the bloodwork, $150 for the required followup. That's $600 that I really can't afford to spend at the moment. Might be an option later this summer, but for now it isn't. I'm actually majoring in Animal Behavior at Purdue (graduate this winter) and I wish there was a way I could say, "Hey, can I use my own dog as a case study?" lol

What do you mean by a "bum back leg"? I'd be concerned that she is more painful than you realize, especially with the growling when being bumped. Dogs express pain most often through behavior changes, especially achey pain, rather than what we might think in our head of overtly painful symptoms.

Never hurts to ask...

A few years ago when she was playing with a foster dog I'm pretty sure she either extended or slightly tore something. She walks and runs normally, but if you go to lift the leg up she gets grumpy and if you hit it hard during play she also gets grumpy. Although I'm sure it causes her aches now and then like my own bum knee does, it isn't anything serious. We just limit her activity on it and that helps. She's been growling when she's resting since before her leg injury, so I don't think the two are correlated. I could try her on pain meds, but I'm not sure if it would help.

It might be worth it to include a trial of a pain medication in whatever else you're doing (at least 3 weeks). Chronic pain, including low-grade chronic pain, can actually change the wiring and the chemistry of the brain and CNS cause everything from depression and anxiety to cognitive impairments. It can also potentially lower an individual's overall pain threshold or causing something called allodynia, which means that normally non-painful things like touch can be perceived as painful.

I truly don't think pain gets enough attention as a contributor to behavior problems in dogs.

I do agree with the suggestions of vet check/pain meds.

You truly have no way of knowing what she feels painwise, and dogs often mask their pain considerably.

Personally, I would go with confinement more than a muzzle. Prevent her form being in situations where aggression might happen. Then bring her out when you're there to watch/identify triggers/counter condition. Muzzling for that could be OK ~ I like the Jafco muzzles.

And tell visitors not to pet her.