Confused on detecting noble metals at great distances...

I've read many posts here and on other forums and beleive that LDL and MFD are not reliable. It would seem to me though that some sort of technology has to exist to pick up metals at some great distance (besides a metal detector). Am I wrong? I've seen some ads on the Gold Gun, etc. that claim that certain metals are conductive and over time emitt some sort of signal (?). Any comments? Is the technology for long distance "grounded" to metal detectors only? I can't believe that Metal Detectors are the only route after decades of electronic TH while technology seems to advancing by leaps and bounds in other fields (maybe its priorities and TH is at the bottom). Some say that Principles & Practise of Radiesthesia by Abbe Mermet shows that metals give off rays(?) that can be detected? any truth to that? Does some have a semi-workable/workable protype on machine that will detect at long distance? Anyone willinh to share a schematic? Thanks! - Shawn.