The FamHist blog site has yet another entry on Grave Dowsing.
This entry has many links to articles on the subject. I believe you'll find it quite interesting.
Dowsing has been used for centuries in this country. Beginning with locating water sources, and even now is used for such, as well as for locating buried electrical wires and telephone cables.
I've seen my own Dad use 2 coat hangers he'd straightened out to locate water sources, as well as water leaks during a winter's freeze and pipes froze. I've also seen him use to straight branches from a tree.
How it works is beyond scientific explanation. Only that it DOES work! Be sure to read the blog entry, and take the time to go through the many articles mentioned. It's quite fascinating!