Speaking of protective dogs, I grew up with a very large shepherd/lab mix, which looked all golden lab except the face, and she was so friendly that we used to joke that she'd probably just lick any intruder to death.
Well, there was a night around age 14 that I stayed at a friend's house four doors down from ours, and I awoke in the middle of the night to see two men trying to break into the front door of their house. I could see them thru the sheer-curtained side lights on the front door, trying to either work on the door knob or just pry the door open. I threw some lights on, and the intruders seemed to decide they'd try another house.
I get home the following morning, and learn that around the same time, our golden lab apparently went absolutely batshit nuts, trying to throw herself thru the glass french doors that let out to our patio. I suspect the same intruders were trying several houses in the neighborhood, and must have come 'round to ours just after I'd spooked them away from the neighbor's where I'd been staying.
It was amusing to hear how ferocious our tame lab had been, when it mattered.