Ummmm.... that is why you clip their wings.

(Though clipping one wing is more fun, that way they flap about in circles).

Even if you clipped their wings in such a way as they couldn't fly anymore, they're still short and covered in feathers which are probably not conductive. The electric fence wouldn't work for many reasons. If you're sure they can't fly, you also don't need it.

The electric fence is for keeping foxes out, not chickens in

That makes sense but idk how effective it is.

Even without clipped wings, my chickens only try flying over the electric netting/fencing when my livestock guardian dog gets a bit too "playful".