I agree there's no way to completely deter aerial predators other than a covered run that you never let the flock leave.
Maybe a dog would help. My dog barks at large birds overhead and the flock runs for cover when she barks but thankfully I don't have a regular ongoing issue with birds of prey. There are plenty of hawks and eagles around but they tend to stay in the valley below our house where there is a lot of agriculture and very flat, open ground.
In the year I've had my flock, we have had only two near misses with a hawk. The experience has made the flock much more vigilant with keeping an eye on the sky and I try to keep the dog out with them when they are foraging.
Obviously any time a flock is allowed to free range, you are taking a risk but every situation is different depending on the predator load in your area. My flock can't wait to get out of the run to forage in the yard so I would have a hard time locking them up 24/7 in the run. If I couldn't let them out to forage, I don't think I would even keep chickens. Makes me happy to see them happy wandering the yard looking for goodies and eating grass like they should be.
On the other hand, if I had hawks or eagles nesting in the perimeter of the yard, I probably would keep them locked up until the nesting period was over. That would be way too risky to let them out in that situation.
