It also feels pretty good to think that your dog wants to protect you, but the problem starts when he decides on his own when you need protecting.
Unfortunately, all the encouragement you gave Fido when he was a puppy led him to think that he gets to decide whose presence is acceptable and whose isn’t.
Now, not only is the UPS guy scared to come to your house, but your family and friends are, too. And what will happen if Fido slips out someday? Are you ready to deal with the ramifications if he bites somebody?
Dogs don’t give up the alpha role easily, so if you’re going to convince your dog that you’re the one who gets to decide who’s allowed on the property, you’re going to have to work to change his thinking. The first step is safety. Be honest with yourself about how likely your dog is to bite. If you’re not 100% certain, invest in a head collar or muzzle.
Once you’ve got the safety angle covered, it’s time to distract your dog with goodies when there are strangers around. In any situation where he would normally show aggression, distract him with some yummy treats. He’ll eventually associate the presence of strangers with good things rather than threats.