I have had German shepherds and can leave them out all day unsupervised while chickens free range. They could care less. Chickens aren't afraid of the shepherds. I have a little puggle that gets bored and will chase them from time to time but doesn't harm them.
I've had 3 German Shepherds who guard the flock;) and doesn't bother them at all, my puggle on the other hand chases them around and is a pain in the butt.