That's one reason why protection dogs tend to work better on their own territory and with their handler standing behind them. Especially if the dog and handler have a strong bond. It gives them something to fight for. As for the selective pressure man puts on animals like elk from hunting, it is a limited form of artificial selection. That's why those populations develop instinctive fear of humans over time. As for the pseudo-natural selection of LGDs, I don't see it as natural selection more like lazy artificial selection. If they had a dog born from an accidental breeding who started killing the herd by the dozens, they would select against those individuals with consistent selective pressure. That may not affect their phenotype or their predator fighting abilities but that's artificial selection to make a herd friendly dog. If one were born who was good with the sheep but terrified of wild animals and was producing a lot of accidental pups who were cowards would they wait for him and all of the pups the starve somehow while the herd was unprotected? If one were a great dog who would kill wolves and bears with ease but didn't produce that with the female he wanted to breed with, wouldn't they try to find another female to breed him to in hopes of capturing the traits that made him great? If not then they would starve themselves and fall victim to the natural selection against foolish humans. So I'd say all the successful LGDs and primitive human shepherds will be using artificial selection for the things they care about, even though natural selection may affect some aspects of the animal.