Pot eggs have worked for us on occasion HeatherB. But we did have one who laid and ate it immediately, so she was despatched. I've heard of people trying a blown egg filled with mustard -but they liked them, which only fuels the egg eating habit. Roll away egg nest boxes can be bought (or made) but can be difficult to fit -I've no personal experience of them.
Hens do peck the eggs to test the shell quality -I've seen it done. If shells are thin they break, so perhaps the problem is a dietary one?