agression only when we're not around

I haven't posted in a long time, but I got some great advice the last time, so here goes. For background you can look up my post "the destroyer" from 2005.

Corbin is now a much better adjusted and much less destructive dog, in fact now he can barely be bothered to get off the sofa without the enticement of his walk or food.

Anyway, when we go out of town, he usually stays with some friends of ours. They have a large fenced yard and two golden retrievers. He's stayed with them like this since he was a puppy, three years now.

The last time we left him, they told us that he had been acting very aggressively to their neighbors. Someone had come over to give their dogs scraps (not something we do, but whatever) and she said that he jumped at the fence and snapped at her. Also the neighbor's son mows the lawn and says he went crazy at the lawn mower and was snapping at him. Our friends say that he will have to wear a cloth muzzle if we want to leave him there anymore. I really don't want to take him away from the "pack" he's had since he was a puppy and quite frankly, as students, trading babysitting for dog sitting is a lot more economical than a kennel.

Now, I really don't want to be the type of person that doesn't take responsibility for my dog and if he is doing this, I want to do everything I can to stop the behavior ASAP. But the problem is, we have simply never seen him exhibit behavior like this with us, in any situation, including when we house/dog/baby sit for these same friends at their home with all three dogs in the backyard. The last thing I want to do is blow this off, but I don't know how to train him against a behavior that we (or the vet, or any kennel he's stayed in) has ever observed. He's not a perfect angel and he does run up to new people, but we've only seen him lick and beg for affection.

We're going to enroll him next month (next available class) in some obedience classes at the local pet smart just to socialize him with other dogs and people, but if his exhibiting "fence aggression" as my friend calls it only when we are not around, what can I do to train him not to?

(side note: Asking the friends to discipline him is a bit of a sticky issue. They "spank" their dogs for discipline and we don't)

I was just wondering, you said that you will be enrolling him in in obedience class to socialize him with other dogs and people. Is he showing some types of behavior that makes you feel he needs socializing?

need for class

yeah, he gets really excited and jumps up/licks new people. That behavior is more under control at home, but if we're out, it's worse.

Also, if he ever gets off his leash, he forgets his name. that's only happened twice, but it was enough to scare me.

One thing you can do is to stage a set up. Leave him at your friends house like you are going away and have someone stage those events that triggered your dog while you are watching from a distance. That way you can see exactly what your dog is doing. Your dog might feel insecure without his family around and so is acting out. You also mentioned that the people who watch your dog spank their own dogs. Maybe they have spanked your dog too and have caused your dog some mental problems? It might be best to either kennel your dog from now on, or find some different people to watch him.

Dogs that are barrier aggressive or territorially aggressive, are usually that way more at home than at someone else's home, but you may want to read this:
http://www.petplace.com/article-printer-friendly.aspx?id=1990
If the dog was aggressive about food, then you need to insist that there isn't any food in his play area, and that no one feeds him treats while he is being boarded there. Food aggression can get ugly, and the dog that doesn't guard food from his owner may do so with someone else, or a child. This book will help if food aggression is an issue:
http://www.dogwise.com/itemdetails.cfm?ID=DTB740
I was uneasy when you posted that these people hit their dog to discipline. I would not leave my dog with such people, as in a moment of irritation, they could hit your dog. Aggression that is met with aggression usually gets worse, and sometimes much worse. You may want to invest in having a behaviorist evaluate the dynamic, and see if your dog is really as happy there as you think.
The Animal Behavior Society web page has a listing. HTH

I agree with seeing a certified behaviorist to evaluate your dog. He sounds like he didn't have enough socialization in this type of scenario. He may be fine in one place or one type of context, but socialization really needs to be very, very broad spectrum because dogs don't generalize very well. Get references and credentials and make sure appropriate methods are used. Don't let anyone treat aggression with aggression. I wish you the best.

thanks so much

Thank you guys for the advice.

We don't have a fence at home, he's on a long lead when he's out, maybe that is the difference.

I think a behaviorist is a good idea (I had never heard of one, this is my first dog). We're thinking about moving abroad next year and the last thing I want is for him to be unpredictable in new situations.

thanks again, if you think of anything else, let me know!