We used a 10 x 10 ft. dog pen for our first run, and covered it with chicken wire. I think the best defense against flying predators is a good rooster who keeps an eye out and gives the signal to go into the coop.
A friend gave us a big roo about 5 years old, and he is a great watch chicken. He was with 3 grown hens for about a year, but I just opened the door between him and about 50 mixed run 10 week old chicks. They seem to be doing fine, I have a large run now that is not covered, he seems to be keeping an eye on everyone, so far, so good. I hope he continues to do as good a job as he has in the past.
And to think, he was going to be "coq a vin".
DonnaBelle