Samson barked at someone entering our home for the first time Sunday (4 months 3 days old). Our daughter had been out of town with friends and busted in the door with 3 "strangers" behind her. He immediately barked, came to my side, and continued barking until I approached everyone and my daughter spoke to him. Monday morning the kid accross the street came in behind my wife and he did it again. Now, in both cases it was someone he doesn't know walking in behind someone in the family. Both times it was over pretty quickly once he realized there wasn't a threat.
Talking with his breeder 2 of his male littermates will also do this, but at least one of his sisters does not.
I have not seen him do this in the yard, but there haven't been any strangers in his yard either. There have been countless kids he knows, and no problems with any of them. Generally speaking, Samson is very chilled out and doesn't bark/show agression toward other dogs or people on or off leash.
I'm perfectly OK with him announcing his presence to strangers in our home within reason.
Our last GSD, Trouble, was more protective. She would bark at horses, other dogs (if she didn't know them), and anything in her yard that didn't belong. Once, the power company changed the time they read my meter. Trouble and our pointer went to the door while i was getting ready for work. I opened the door and let them out not realizing the meter man was in the middle of our back yard. Trouble took off to him and circled around him barking, hair on back up. Scared the heck out of the poor guy, but she didn't bite. Just circled him barking until i came out and talked to him.
She also jumped out of an open but screened window when she saw me petting another dog by the street. Kind of crazy, but she was a good dog.
Before my wife and i were married she lived by herself in a large, older home that had been cut into 5-6 one bedroom apartments. One night she had a knock on the door around 4 AM. She not very intelligently opened the door with just the security chain latched. On the porch stood a large man who demanded to use her phone. When she told him no and attempted to close the door he pushed it back open, and no doubt was capable of snapping the chain. Buck, the 40 LB pointer with 3 good legs charged the door barking and the man ran off. For this reason we do not mind Samson "announcing his presence" when someone enters our home...again, within reason.