One of the recent (hot) threads has several posts about free range chickens and some of them being predated (fancy word for eaten) by hawks. There is a simple fix for this problem: Provide a shelter that the chickens can run under when they see anything in the sky that scares them. They have a natural fear of flying objects and will run for cover. If there are no bushes or trees, just make a low (less than 3 feet tall) shelter or lean-to, nothing fancy, and that will do the trick. If a large pasture (over .5 acre) then at least two shelters, spaced evenly apart. Make it large enough that the chickens can all get under the roof and not be crowded. They love shade on a hot day, too.
I’ve heard that a few large geese would deter hawks, but I’ve never tried it.