IT IS PREY DRIVE YOU DOOFUS.
You CANNOT TRAIN PREY DRIVE OUT. AT ALL EVER. That DOES NOT MAKE A DOG AGGRESSIVE.
All you can do is manage it, and train the dog to listen. And anyone who thinks that all the training in the world is going to teach a dog to listen all the time is crazy. Training a dog to be 99% reliable is brilliant training. But you still have that 1% that you cant count on.
And it is NOT like Dekka is letting Snip go around the neighborhood killing cats. What can she really do from across the yard if a cat wanders in the yard and Snip gets to it first? Three to five seconds. That is IT. Some people cant even REACT in three to five seconds, let alone make it across the yard to grab a dog intent on killing a cat.
Wow is all I have to say. Some people in here are clearly looking at dogs through rose colored glasses. Grow the **** up. A dog is a dog is a dog is a FCKING DOG. DOGS CAN AND DO KILL THINGS. Oz has killed SEVERAL SQUIRRELS. Should I only allow him outside with a muzzle on? I'm sorry, but I'm not going to do that to my dog. As a matter of fact, I don't even own a muzzle. With other dogs around that puts him into a defensive anxious mode, and even MORE likely to snark/snap/bite at another dog. And then what? The other dog takes offense and attacks my dog, leaving him unable to even defend himself? I'm sorry, but I care WAY more about my dog that to have something like that happen.
Oz is under control in public and private situations. AT ALL TIMES. Even in our yard he is under control, and especially everywhere else. But if something triggers his prey drive off leash in the yard, squirrel, bird, or cat, I'm sorry, but there is not much I can do from the patio, and I have zero chance of making it too him in time to save whatever it is should he catch it. His prey drive is not extreme, but he IS part terrier and therefore prey drive is something I have to contend with at all times. I REFUSE to constantly have a leash on him in the yard, where I know he cannot get out of, and wont leave no matter what. Yes, I know he will not leave, no matter what. If a squirrel or cat makes it to the fence in time, it is home free, he will not go after it after that.
But if it can't get out? I try my damndest to get there and stop him, but I don't always make it in time. He has never killed a cat, and never even closed with one, but I have no doubt if he did corner one, and it fought back, he would turn on even more. He has killed many many many squirrels, chipmunks, moles, rats and voles. He keeps our old house rat free even more effectively than our cat does. It is instinct. I certainly DID NOT TEACH HIM to do that.
So prey drive makes him aggressive then? My my my, it is a sad sad world we live in.