Silly Chickens! For birds that can't fly very well these girls seem to do very well at getting out of their yard.
We replaced the 2 ft fence with a 4 ft fence. That kept them in for maybe three days. Then I would catch them hopping, with full speed ahead wing flapping, over the new fence. A trim of the wings help for another two or three days, then I caught Queenie jumping over the fence and landing on the exterior nest box. Of course when one does it they all get the idea and I started finding two or three getting out a day.
I added two rows of cord to the top of the fence, attached to the fences poles, which added an extra foot of height to the fence. Worked like a charm for two or three days, then I started catching one or two chickens out each afternoon. I watched and watched but they never escaped while I was watching.
Now as much fun as I have watching the girls go about their business I can't watch them from Sun up to Sunset, or I'd never get my work done. I was beginning to think I would never figure it out until PeterC just happened to look out the back door as the most recent escape took place. The entire flock cluster very tightly together at the base of the fence and suddenly one of the hens came shooting out of the middle, and straight over the fence, like a watermelon seed pinched between your fingers.
So, it seems the girls have figured out how to work together to get out of their yard. Fortunately, this technique only works as long as there are enough chickens inside the fence to toss one out. Once you get three or four girls outside the fence the rest stay put. Unfortunately, I have to come up with an even higher fence to keep their feathery bottoms where they belong. Maybe little concrete shoes would work.