Tesla just turned 4 this year and since then she has become very aggressive towards other dogs while on walks and at the dog park. We used to regularly visit the dog parks around us without a problem. Now she will barely let a dog approach her without growling and snapping- and the other dog can be completely calm when approaching her. She won't even sniff/let the other dog sniff her before she's set off. I'm not sure what to do to break this new habit of hers. She never responded to clicker training as a puppy so I don't think I can go that route. Does anybody have advice for this?