Have you considered a plastic owl? Crows here will steal chicks, they never try to take on the roosters, they just outsmart them. While a hawk flies and hovers before an attack the crows just sit in the trees and wait for an opportunity. Hawks will not dive into cover they cannot fly out of, crows will dive in cover and chase chicks into the open. I know this sounds cruel but I try to hatch twice as many chicks as I intend to keep to account for the loss. I would rather have the crows than the hawks that will kill a adult bird. The only other choice to free range chicks is to build a light tractor that you can move several times a day to simulate free ranging. Or maybe in the open area make some supports to suspend dear netting over the ground.