We have a variety of chicken breeds and never had an egg eating problem until we added White Rock hens last summer; I don't know if the behavior is breed related. We never had nest boxes - for years the hens picked a bit of mulch in the coop and layed wherever, but we put them in the past year to see if it would increase egg production. Production was fine but retrieval was zip because they seemed to eat each others eggs. I've taken the nest boxes out, and now everyone is laying where they please again. The only eggs that seem to get eaten now are those that are layed where the nest boxes used to be. I suppose the nest boxes set up some sort of territorial behavior. I'll certainly try making an egg with mustard in it. Can't hurt. It's so annoying to go to retrieve eggs and find the White Rocks having a feast on several crushed eggs. Any other advice would be welcome.
Did you acquire the white rocks as adults? If so I would be willing to bet that their previous owner got rid of them because of their egg eating habit. The behavior is not breed related.