My 7 yr. old B, Rocket, is a fence fighter. At home with the 2 shih tzu's next door he will race up and down the fence, hair raised, and attack the fence. If my female, Rumor, is helping, he will turn and snark at her too. At daycare, he bit one of the helpers when they were bringing a dog in. It is always when he is at the fenceline or on a leash that this occurs. What do I do when this happens?