Eating rocks, a condition called "pica" (aka non-edible items) generally signals either a medical cause or behavioral reason. First, call or visit your vet since since medical causes for pica include scary and serious health conditions. If the vet rules out medical reason, then it's probably behavioral and will require training to help the pup. Ask your vet or check reputable online website for resources and referrals on how to resolve the pica problem in the short-term and long-term.