I found this suggestion for metal detector testing and practice several years ago, and made several strips. There is duct tape on both sides.
The enclosed items can be labeled, scanned, and then for a test, flip the strip unlabeled side up, and identify.
I made 7 strips, each about 6 feet long, and included various challenges including, for example, covering silver dime with pull tab. Separation was about 14 inches between affixed targets. Very handy for learning and refreshing skills of target ID.