It seems clear to me that using two copper rods (they call it "Witching" around here) is totally bogus. The claims are 2 bent wires can:
- locate concrete pipes, clay pipe, plastic pipes, power lines...anything, any material your worried about.
- It can locate water,
- No one can say how acurate it is,
- No one can tell you how deep it can detect things,
- It works better for some people than others,
- No one knows how it works.
People forget the times they get it wrong. There's a driller I worked with that remembers all the things he didn't hit, but never mentions the phone lines he drilled through in our parking lot during an open house demonstration. (I watched him witch that spot - who needs a utility locate?)
With a few surface features people who have been around usually figure out how things are run, and can get it right on that alone a lot of time. Lines aren't just randomly put in the ground (Most of the time anyway).
I think witching is a poor and dangerous pratice.
This would be a good one for mythbuster.