Focus Information Agency in Bulgaria relates the story of a truffle hunter and his trained dog digging up something other than fungus in the Stara Planina mountains. According to the story, the man dug out a truffle that his dog sniffed out, and found 16 silver tetradrachms dating from the Roman Empire in the hole. The coins are said to be "perfectly preserved," and it is supposed that they were in a purse that has long since rotted away after they were buried. The man brought the coins to the National Museum of History, in Sofia.
Sometimes you don't even need a metal detector to strike underground riches, it seems. Just take your dog with you!