My run is about 40' x 50' and 8' high chain link fence. No netting or cover over the top. Large coop sits right in the middle. Been like this for about 7 years.
Why? Because we got the chain link for free. Came from a highway construction site, and they were going to dump it. We happened to have 12' hedge posts available, also free from a relative who was clearing land. We needed to build a run secure from coyotes, fox, raccoons, and raptors. 2+2=4.
I'm surprised we don't have more hawks carrying off our chickens. But I think it's because the fence is so high, they can't make a running start carrying a load to clear that fence. I shot one once inside the run, reading the menu specials for the day. But none since. They fly overhead, announce dinnertime to their buddies, the chickens run for cover, and that's it. None has tried to land inside.
Hasn't kept the raccoons, out though. They climb right over and clean up the feed scraps every night. Groundhog forced his way through the gate until I fixed that.
I worry foxes will get in - I understand they can climb quite well. Defense is to keep the coop ultra-secure, and I limit free-ranging so as not to set a regular schedule or pattern a fox will recognize.