Daisy did put on a pretty good display a few months ago, 2 guys came to do service on our water conditioner. She didn't let them in and I had to physically restrain her. It was more of a "who are these strangers coming into my house" than "I'm going to bite these guys who are coming in my house". It was territorial though, that's for sure. Gunnar was easy, he'll let anyone in if he sees me being calm with the person, but he won't take his eyes off them. I had to keep him from going down in the basement to watch the repair guys, because I was working and didn't have time to sit down there with him. Another time a few of my son's friends were over doing some recording in my little basement studio, and a few other friends showed up. Gunnar went downstairs and laid by the door, watching them the entire time, because he didn't know them.
Doberkim, "come one step closer and I'll kick your ass" is a type of avoidance by the dog. Some people will see their dog back up on the training field, and think "he's luring them closer so he can bite" when really, they are showing a degree of avoidance. That dog should be out at the end of the leash, straining to get to the decoy if that is the exercise. The dog should be acting like, I don't care where you are, I'm coming at you and I'm going to kick your ass. I can have Gunnar in a down, not barking and being very calm, but not taking his eyes off the decoy, the decoy can be jumping around and making noise, agitating him, and as soon as I give him a "pas auf" (watch), he leaps up and hits the end of the leash, with an aggressive bark, trying to get to the decoy.
Your comment about people who don't understand what protection is, confusing a fear based reaction- growling, barking, hackles up, showing teeth, with protection, is completely correct. It's all a bluff but if it works, then the dog did his job.
Recently my trainer had 2 dogs dropped off at his house, a divorce/no home to keep the dogs situation. One was a 2 year old GSD, fairly well trained, good with kids, and in general a good pet. He wanted to test the dog's protection ability before he placed him in another home- thinking that if he was good, he'd keep him and train him. The way you test the dog is to back tie him, and then agitate, and watch the reaction. You start out far away, making noises like cracking a whip, shouting, and watch the dog. A dog that is interested will come out to the end of the line, bark, but not show teeth, raise hackles, or turn their back. You work in closer, not confronting the dog- avoiding eye contact, moving side to side and not straight in which puts the dog in a defensive posture, and keep testing. This dog went straight into fear and avoidance- he wouldn't look at the decoy, he paced around looking for an escape but he couldn't because he was back tied. When pressure was put on him- whip cracking at his feet, he raised his hackles, bared his teeth, growled and barked but would not come any closer to the decoy. Eventually he jumped over a 6' fence to get away from the threat. His reaction was typical of a dog that didn't want a confrontation and showed everything he had to avoid it. Most people would see the teeth, hair, and sounds as protection, but the dog really was showing fear and avoidance.