My oldest one(non GSD) generally likes everyone, so if she barks or shows signs of not being comfortable, I know something is wrong. The golden thinks he's a rott, he really loves everything, but one wouldn't know that if they tried to approach me..he is probably the best deterrent vocally. The GSD is quiet, but will stare someone down and she doesn't let up until they are gone. Most people are afraid of her, but she isn't a mean dog at all. If all three of them are together in the house and barking, I can't imagine who would be stupid enough to try to come in. So yes I do feel safer with them, even if all they do is alert...most of the time that can be enough.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD