We've been having trouble
with one of our hens flying over the 5 foot high pasture fence.
It's the first time we've had
to clip a chicken's wing, and we both considered this a last option, but
she's had more than one second chance.
Some folks say to just clip
one side, which prevents flight due to imbalance but still gives them a
few extra inches of feather punch on the other side if they have an
encounter with a predator. If she keeps flying over we'll clip the
other side.
My observation is that clipping one wing causes imbalance in flight, clipping both just makes flight more difficult, but often not impossible for getting over a fence.
I have also seen a chicken that figured out how to compensate for the imbalance caused by one wing being clipped. The person doing the clipping always did the right wing. Switching to clipping the left wing fixed the issue. So I suggest alternating wings.
If it keeps on escaping it may be best to have a fresh chicken for dinner, before it gets eaten by something else.