Kentucky National Guardsmen searched bags and passed metaldetecting wands over race goers, while raincoats, towels and small cameras were being inspected.
Dr Bowles said that as well as providing a clearer picture of the history of Mantle Walls, he hoped it would help stop illegal metaldetecting in the area.
Although that is two to three times the cost of a metal detector, it is less than the price of the fancy explosive-sniffing equipment that is the main rival technology being developed for detecting metal-free mines.