I agree with you guys. This is defiantly a territorial behavior. He is just trying to protect you and his home. You have to show him that it's okay if he alerts but that YOU have the situation under control and when YOU tell him to stop he will. My dogs do the same thing so I say "okay, good job" to let them know they did well then tell them to back off while I open the door. Enrolling in a basic I=obedience class would probably be good too.
