By sky, I mean hawks and such. We have a pretty good sized run, and the coop sits in the middle of it, and is pretty high up. It isn't the ideal situation, but it is our situation. The Walls are about 6 feet high. The one question is what to put up top so that the birds of prey can't come in? Oh, yeah.. has to be fairly cheap in that my hubby is already complaining on how much this is costing us.