Neil in SJ:
To state Piney Boy's comments more plainly, when you go out metal detecting and you begin to remove objects from the ground, you are destroying the spatial context of that object and how it relates to objects around it. If the site remained undisturbed until archaeologists excavate it, they will record X, Y, and Z coordinates of all objects found and then map them, graph them, and catalog them to gain a full understanding of the relationship between the artifacts uncovered. Random searching with a metal detector destroys the opportunity to perform such an archaeological investigation. Furthermore, modern federal regulations require a full cultural resource investigation prior to the construction of any highway or bridge.
You state, "Metal Detecting preserves history, it DOES NOT destroy it." However, it preserves history for who? The guy who finds the artifact? In finding that artifact, you HAVE destroyed how it relates to other artifacts still in the ground. So, it DOES destroy history.
That being said, there is a group using metal detectors in a very scientific manner at the Monmouth Battlefield in Monmouth County. This group of dedicated volunteers have mapped artifact groupings and aided historians and archaeologists in gaining a fuller understanding of precisely what occurred during the battle. Using a combination of metal detectors and other scientific instrumentation, these guys do plot full X, Y, and Z coordinates for the objects before ever removing them from the ground. They can map the full array of artifacts prior to any disturbance. Once they remove the items from the ground, they catalog each item and then develop a hypothesis based on all the evidence. This is a great use of metal detection technology!
Jerseyman