Well, a guardian dog (such as a Great Pyrenees) will deter a hawk crows, etc. They tend to watch the sky as well as distance and seem to understand that threats come from above. They run and chase and bark it away. These are >100 lb. dogs so they are large and fast. The would absolutely attack a hawk if it lands on the ground. In lieu of that, we are always present when they are free ranging. I mean literally standing within a few feet from them. We don't have a rooster so I serve this purpose. We have a large Red Shouldered Hawk that circles and the other day it came ripping through the yard about 10 feet above the chickens. They bolted for cover and I started running to make sudden movement. It does check back from time to time. I see where others say a hawk will attack even if they are present. It would seem if I am standing within feet of the chickens that should be deterrent enough, I'm hoping. If a hawk attacks one of my chickens, it will be a sorry day for the hawk.