Our little pomchi chased a German shepherd all the way across a very large park, barking her crazy head off the entire time. She was normally a very obedient and sweet girl, but would just completely lose her fucking mind whenever she saw another dog at the park. We had to stop letting her off the leash anywhere that other dogs might be. If she was on her leash then she would be chill, and just wag her tail and say hello. But the second her leash was off around another dog, she turned into a psychopath.