We have a chicken tractor and 6 chickens, young hens. We've always let them roam in the yard, but needed to be out keeping an eye on them because our lot is only about a half acre and they want to wander to the neighbor's yards. Yesterday my husband brought home some portable fencing to give them a bigger run and me the ability to let them out when I can't stay out there and watch them. It took about 30 minutes before some smartie chicken figured out that she could fly out over the fence. Is there any way we can stop them from flying out?