4 mths ago i rescued a gsd from animalcontrol a day before euthanizing him.i was very surprised when i took him home (thunder)because he knew all commands,hand commands,he gets me when he has to go outside, he walks very well on the leash, and even without leash, he doesnt leave my side.He gets along great with my two chihuahuas, and doesnt care about any other dogs. Meaning when we went on our daily walk,a loose dog came up to him barking and he just went on, paying him no mind. Make a long story short, he is very well behaved and listens to everything and is very smart. BUT when someone is at the door he goes crazy and his hair is standing up. When he meets people outside he is good with them, people who cme to the house is another story. My question is how can i let someone in the house without fearing that he will bite them?when i have workers coming, i usually put him in the backyard. Any suggestions on how i can tell thunder its ok for people to come in the house when i am home?