Our roosters trained us and the dog with their alarms. I point to the sky and get the dog going. Now, the dog will run around and around barking up at the sky, crows, hawks buzzards whatever. My backyard is mostly open but the birds have plenty of places run and hide - which they do. I was thinking that the openess makes it easier for the chickens to spot the predators so they can scoot under something... as opposed to a wooded yard where hawks can sit in the trees more sneaky like. Some one might be able to input on this theory before you move your free ranging to a more open part of the yard, but in my situation as long as they have their rooster, and a place to get to quick and hide, I prefer it being more open. I just think they can spot the hawks easier. I have some lattice work leaning against the fence that they like to go under, and a hinged framed lattice that makes like a tunnel they go under to get across the middle of the yard. I also have 3 cats, don't know if they help or not