some years ago I did an exhibtion for littlehampton museum on a company
called duke and ockendens, who specialised in drilling water wells and did
so all over the world. For many years they used dowsers to find water.
However, one of the people I interviewed was a retired engineer who actually
drilled the wells and his view was "the drill finds out the dowser" -
according to him, in most cases, dowsers failed to find water. so I guess
the same may be said for archaeology.