This is one expensive treat that Golden Retriever Sollie snacked on the other day .. . a three-carat diamond. A dealer visiting Robert Bernard Jewelers in Rockville dropped the "treat" and the doggie jumped on it -- thinking perhaps it was a marriage proposal.... Maybe, on second thought, dog-in-jewelry store not such a good idea..... The diamond was retrieved, three days later, by store owner George Kauffmann, when it exited Sollie's other end.....