My father-in-law's experience with dowsing might be interesting. He was an engineering supervisor with BR, and an experienced plumber. On many occasions he was called upon to search for long-buried pipes and culverts which had been underground for over a hundred years; he used a combination of skill, observation and common sense to find these hidden structures, with considerable success.
The local area manager had heard good reports about dowsing, so he sent several of the civil engineering staff on a dowsing course, trying to find buried water and cables. After a while, everybody else on the course was reporting success at finding the hidden pipes, except my father-in-law, who just couldn't feel anything using the rods.
I suspect (though I can't prove) that my father-in-law already knew where to find the pipes, by using his trusted observational skills and knowledge of plumbing; but the other staff who were not so accustomed to locating buried infrastructure were subconsciously observing the same clues, and using these observations to find the pipes anyway. The dowsing rods were their way of reinforcing their subconscious or half-formed impressions of the underground infrastructure; whereas my father-in-law was confident enough not to need the rods, so he ignored them.
Or, as he put it, 'they don't bloody work for me'.
