I have a 3 year old Coton de Tulear who is amazing in every way except when the door bell rings and people come over. He barks like crazy and he will jump on whoever is at the door and bite at their clothing when they first come in. Once he calms down he loves everyone and is very friendly. He is only like this when people come into our house. Any suggestions? We now keep him in his cage if we are expecting people and he comesout once they are in the house and settled.