Our neighbor that lives behind us has a little mixed black dog, she has found her way under our fence. Today Harley took off after her, she was not being a threat at all, but he was giving it all he had, she scurried off under the fence. Last week he stomped a cat from the dairy farm that jumped the fence. This is new to us, because he has never done this. Sissy is a small dog and he has NEVER tried to stomp her. Is this normal and what would cause this behavior? I know it is his pasture and his home, but is there a way to stop this behavior?