There is no way to keep them 100% safe - even those who don't free range lose chickens. But you can do some things to keep them safer. Make sure you have a coop that they can go into that you can shut at night. That will keep the critters that most commonly roam at night away from them (coons, possums, fox, skunk, coyote). Sometimes the "night" critters also come out during the day, but they're usuall a problem at night when they have lots of time to ponder upon how to get to those tasty morsels inside. During the day, hawks could be a problem. Make sure they have plenty of cover to run under - bushes, small sheds, even planks set across cement blocks will work. Stray dogs are a problem that's hard to prevent, but if they're free ranging, hopefully they can get away istead of being cornered like they would be in a pen. Not everyone can guard their chickens all day, and I'd be very careful about shooting anything that comes swooping out of they sky toward your birds. It's most likely a federally-protected-very-expensive-if-you-get-caught-shooting-it hawk or eagle. If you do shoot such a bird, don't announce it on a public forum or tell anyone that you've done so.