I have 2 really sweet barred rock hens. They are about a year and a half old. I think they learned this behavior from some wyandottes I had and rehomed for this reason. I have not gotten eggs from them for several months and production from my other hens is down. When I let them free range and keep the other hens in the coop, my production is back up. So I know who it is. I suspect their shells are soft. I give 20% protein and provide oyster shell in addition to crushed egg shells. Not sure if they are just not absorbing the calcium. I have tried clipping their beaks, giving them a flock block, giving them ceramic eggs, using nesting box pads, and rollaway nesting box inserts. They are laying outside the box specifically so they can break and eat them. The only other thing I can think of doing is putting them in a little pen outside my back door so I can watch them very closely to try to figure out how exactly they are doing it so I can come up with a better plan. Any suggestions??