Well, I obviously wasn't very successful with Rosco, but one tip sticks out in my mind that makes sense. Whenever Rosco would do that, I'd pet him and coo "He's a nice kid Rosco..." -Basically trying to reassure and comfort him. The behaviorist or trainer (don't remember which) told me that is totally wrong. I was rewarding his bad behavior. She told me to snap his collar and give a mean stern NO when he shows signs of aggression.