If you keep your food and water in their run (or near it), they won't go far. They know where the food is and shelter.
We've lost several chicks under 12 weeks old to hawks. We also had a feral cat eating our chicks, but he took down our full grown chickens, too. We still free range, but have at times kept them locked up when we saw the cat around or lots of hawks were around. The hawks seemed migratory, as in the spring and fall there are more of them than other times of the year. I don't trust the hawks, but they seem to leave our full-grown chickens alone. We also have two roosters, perhaps they help.
You can also train them to come to you with corn. Do this once or twice during the day and see if you are missing any.
Be prepared for the reality that free-ranging does equal losing some birds. We'd rather they live some life of freedom and potentially get killed than be trapped inside a coop and run for their entire lives. We didn't lose any chickens to predators for about 12 months at first.
I let mine free range when they are a week old in the warm months. You will lose some birds. I think that they are definitely old enough to watch their back.