It depends on more than just having a rooster. Depends on the roosters themselves (not all are created equal), depends on how much cover they have to hide under quickly, etc. As I said, we've been very fortunate but you can't free range forever, especially in the mountains, without having a loss eventually. I've seen hawks dive on the birds, but the rooster intervened and he never touched one. Had that fox's den I mentioned on the property. We have all sorts of predators, including coons, possums, fox, coyote, roaming domestic dogs, owls, many different type hawks, mountain lions, bears and now, I've been informed that we also now have fishers in this mountain area (as if we didn't already have enough to worry about). It's possible, however, to free range chickens without having constant losses, providing you pay attention to some details.
At night, they are in predator proof coops, but during the day, we rely on our roosters coupled with good cover to keep them safe.