There are a few things you can do. One if possible string white clothes line in open areas, as much as possible. This works very well, what your trying to do is make the hawk navigate his dive. This gives the chickens time to seek cover. If you don't have a roo get a good gamecock once he establishes his flock he will give a warning crow sending the rest of the flock for cover. If the hawk is stupid enough to try to get a chicken once he is on the ground, he will be dispatched quickly by a good rooster. This is legal and you cannot be fined if your rooster kills the hawk, just call your local game warden to pick the hawk up. A dog will decrease hawk attacks, but then you may have to worry about the dog. It is legal to harass the hawk from your flock, in fact before getting a permit to destroy you must show that you have tried to use other means to scare away the hawk. Buy a fog horn from a marine supply, this will give hens a warning and it will scare the hawk. Throwing things in the air like CDs that will scare the hawk works too. You will not get anywhere near the hawk they are too high, but the hawks vision is good and just doesn't take the risk. If you do not have chicks, and do have crows put out corn for the crows. Crows hate hawks and will attack them in the air, especially if they have young of their own. BUT I have seen crows take chicks.
Be careful that hawks have attacked people, they can leave nasty head wounds. My MIL was attacked by a hawk in FL and had to be taken to the hospital. You have a legal right to protect yourself from any predator even a protected one.