Sensible post Sweep I only slightly disagree on one point /suggestion .
"Nor is there any doubt that people can trace things they don't know are there by other means. " .
Water is one thing but previously unrecorded and unsuspected archaeology is a bit different ,any examples ?
I've read Sweep's post as there have been unrecorded "things" found and been shown to be found....actual physical tangible provable "things"...not spurious selective energies, ie...energies selected by the finders (be they genuine, self-deluded or charlatans) and not as some claim the energy selecting the finder. I hark back to an episode of Time Team where dowsers were used to trace lost walls in an area where geo-phys was unable to be used...they had definite "rod-readings" and were sublimely confident of their abilities(even Tony Robinson had "results" when offered to try for himself).....and when the excavation revealed absolutely nothing...the dowsers gave some really lame excuse...sort of made their excuses and left.