OK, I've just gotta say this. Chickens can FLY! With the nestin boxes being so high up on that wooden fence, just what makes you think the chickens won't just fly over that fence to someplace else? If you clip a wing, they won't be able to get to the nest box. If you don't cover the tops, or even if you do, it is just a short hop to clear the top of that wooden fence. I have my henhouse on stilts 3+ feet off the ground and I have a ramp for them to walk up into the henhouse. I still have one or two hens flying up on top of the henhouse, easily 8-9 feet off the ground. I have my chicken yard enclosed by a 6ft chainlink fence and have even seen a chicken walking along the roof of the house (MY house). So, I clip one wing of each bird but it still doesn't keep them from trying to get the highest spot around, which is naturally what a chicken wants to do. I'm just trying to point out that if something isn't done, those chickens could soon be wandering the neighborhood. Chickens are pretty self-sufficient and it doesn't take much for them to go "wild" on ya. This is all in addition to the already-pointed-out dangers of predators, and don't forget neighborhood stray dogs either. It wouldn't take much effort for a nice-sized dog to push its head through that wooden fence.