Believe it or not, in the mid 70's when I was a kid, my uncle was an electrical engineer for US Boat doing sonar work for the sub fleet. He built a fairly sophisticated metal detector and we just had to try it out. Off we go to Gettysburg naively unaware of the law....we were detecting between the Angle and the PA monument. You could not move an inch without finding a bullet, part of a bayonet, horse bit, artillery chain or buckle. I would imagine the same at Devil's Den, maybe more so.
A park ranger came lumbering out of the maintenance area behind the ridge and told us he knew we were fairly ignorant of the regs and gave us a break. He asked what we found and as I was holding a snaffle bit, said "just this", he chuckled looked at my Marine fatigues that looked like jodhpurs with all of the pockets full, told us who to contact if we wanted to legally hunt in the area.
The real sad part of the story, my mom threw out all that we found 5 years later when I went off to school, along with my baseball cards.........