Really, there is no such thing as an empty hole. If your dowsing rod locks onto something, there is something there. In my years of map dowsing, I have found several types of hot rock that give me the same signal as gold. Those that I have found, I can discriminate. Therefore, if you have a map or photo of a hot rock, I would like to hear from you. Maybe I will be able to discriminate these in the future. Thanks, Al