other dog aggression

Question
I have a pit,jackrussel terrier,lab mix.I adopted her and her pal a beagle mix from a shelter when they were 1 year old three years ago.The pit mix is other dog aggressive On leash and in the house but thus far not off leash  all be it never intentionally off due to the danger in it. out side.We have tried shock collars with limited success.treat and positive reinforcement training,and sociolizing.We have also went back to basics with obedience training with one other dog in class.I do not wish to put her down but she has started doing warning "nips",no actual contact,when wanting to get at another dog.Can I still help her or is it just too late she is now 4 and we have tried for three years.

Answer
You should never use punishment to deter aggression. Think about it. A dog sees another dog and thinks that dog might be a threat and growls to warn the other dog away whereupon she is immediately shocked or otherwised punished, thereby proving in her mind that yes, indeed that dog was a threat and other dogs probably are too and she was right to warn the dog away and next time should probably skip the growling and go straight to the biting.

Most dogs are aggressive on leash. There are several possible reasons for this. First, the leash is restricting so if the dog has any nervousness about another dog at all, she is going to be made even more nervous by the fact that she knows she can't escape. Second, the she is attached to her human, therefore she is honor bound to protect you (especially if she isn't clear on the fact that you are in charge) if the need arises if she feels that that's a possibility at all, she's going to be on the offensive right away and Third, when two dogs approach each other attached to humans by a leash, the humans are often nervous and hold the leashes tight this makes dogs approach head on, which is an aggressive approach and makes them hold their heads higher than is polite in dog society. A dog on approaching on a tight leash is forced by that leash to give off messages of aggression and intimidation which, unless the other dog is more inclined to roll over and play sub, is going to to inspire the other dog to respond likewise.

The best thing you can do now is to ensure that your dog knows that you are in charge and that YOU are responsible for the protection of yourself and the house. Read this article for information about that http://www.thegooddogjournal.com/2009/02/whos-boss-establishing-pack-leadership....

Do not approach other dogs on leash unless your dog already knows them. Do try socializing her off leash. And if you would like to bring a new dog into your home, introduce them in neutral territory and then walk home together.