I think it can be a tricky one to solve, have heard various methods of filling eggs with curry and stuff the chickens won't like to prevent it. One way would be to craete a rolling nest box to stop them getting at the egg once laid. Or you could try being really vigilant and checking more often for eggs to get them before they do so to speak.

I do belong to another chicken forum which has loads of experts on, pm me if you need details.

janeyo