I rescued my pup a year and a half ago at 6 months. She's a 18lb Jack Russell rat terrier mix (possible other breeds) with tons of energy. We've been going to the dog park multiple times a week since I've had her. She had always been very submissive, always going belly up! Never got aggressive unit recently she has started to get more defensive. She's never hurt another dog, but shows all her teeth and lunges at them. She is clearly not happy and I lead her out of the situation asap. It tends to happen when she feels ganged up on and is surrounded by multiple large dogs, which I understand. It can also happen 1 on 1 depending on how the dog approaches her, or if they are playing aggressively. Most of the time the other dogs don't mean any harm. I don't want to scold her because I know she's trying to defend herself, but she looks so nasty and I want it to stop! She was actually bit today at the dog park and was scared of every dog there after. I want to help her, and have all positive reactions!