I am not sure if Samson would attack an intruder. He will make his deep bark if the UPS man pulls into the driveway, but if he is outside when he pulls up, he would rather lick him to death. One time we had a complete stranger in the house. Samson was not aware that we had a visitor. When Samson walked down the hall towards us, he nearly hugged the wall. We looked very timid. Our friend, at that time a stranger to Samson, said, "What a wussie." We laughed at it because Samson, the big guy that he is, did look rather funny.
Dogs do sense a bad person from a good person in many instances. I had an American Eskimo that didn't like a particular friend of my son. That kid broke into our house later that year, when my dog was in her crate, and I have since said that the dog knew the kid was up to no good. She detested him and it was obvious.
Delilah, well, I do not know what she would do. She lets Samson know when he is too rough with me, but I have no idea if she would protect.
Mary