We always have to be on the alert for predators. I have to supervise mine when they free range anymore. Hawks attacked one of my breeding pair, on Thanksgiving day. Scared the crap out of those two. Now they won't free range unless they can see me out there with them.
The rest of them were not attacked, but they know to keep their eyes open for hawks and dogs. The big flock (of 10) has 2 roosters for alerting etc....and the 7 hens can go about their business of digging and scratching, dust bathing, and laying eggs. They know the roosters will alert them to any danger.
Oh, DH does dog alert on weekends and weeknights with his hunting rifles. We have dogs, fox, possum, raccoon.