Ah, hawks. If you are lucky, you just won't have that problem. When we lived in town we didn't, for whatever reason. Now that we are in the country -- yes, we have hawks. We freerange our chickens, and have lost one to a hawk since moving here three years ago.
Options for protection all seem to have big downsides. You can keep your chickens in a hardware cloth-enclosed run all the time (expense to build, chickens can't roam); you can get a rooster (they are loud, may not be allowed, good but not perfect hawk deterrent -- they can't be everywhere at once); you can try a livestock guardian dog (expensive, frequent barkers, require training, not ideal deterrent for an aerial predator). You can also go with very large breed chickens (Jersey Giants, Brahmas) in the hope that their size alone will deter smaller hawks. But large breed chickens will not have as good an egg-to-feed ratio, and size is not a foolproof deterrent either. The chicken we lost to a hawk was one of our largest ones. And our tiny little Crested Cream Legbars are batting 1000 so far against the hawks somehow.
If you intend to let your chickens out of the run sometimes, probably your best bet is to provide some cover for them and then let them take care of the rest. The pasture where our chickens range has trees, bushes, brush piles, and loads of hiding places. We have lots of hawk activity here, and the chickens are very very good at spotting them, alerting the flock, and diving for cover. If we only lose one chicken every few years, I can live with that.
