Clip their wings. I gives you peace of mind and gets the flying notion out of their heads.
I also clip both wings. You hear alot about clipping one wing to unbalance them, but it is very surprising to see one done that way - when it flies up to the fence top and perches on one of the posts!
You feel pretty helpless standing there while it looks at you, deciding what to do next. It seems no one told the chicken that it wasn't able to do that anymore or that it shouldnt be flying around in the first place. I started doing both wings after that happened. Assume nothing.
CAVEAT: Clip their wings only if your chicken yard is predator proof. Flying is a survival tool for chickens. If you deprive them of it, make sure nothing can get them.