I have a Hawk that hangs around but my chickens are so big I don't think it could pick them up! And my Roos set off alarm every time he comes around.Hawks are just about the only predator I haven't had problems with. Roosters make pretty good warning systems for hawk attacks as well. He'll let your girls know when to hide. I've also heard other chicken folks tell stories of roosters fighting off hawks. So maybe you need a big bad rooster
Personally, I've come to terms with a certain amount of loss that goes along with free ranging. I lose a chicken or two every year. But they're so much happier and healthier when they free range. I love watching them play in the yard.. I have a pretty large covered run, but they look so sad, watching me through the fence. But I only let mine out to free range when I'm home, so mostly just the weekends.