Q. My yorkie get angry when visitors leave at the door. He tries to bite their feet
A. Put him on a leash when it is time for your guests to leave. Keep him some distance from the door and tell him to sit and stay (I hope he has already learned these commands . . . If not, you need to teach him now). As long as he is sitting quietly, reward and praise. Continue as your visitors go out the door. When the door closes, give losts of praise. After several times of this, he will associate people leaving with goodies for him, and the biting should stop.