Why are they booby-trapping trails? Seems kind of silly, because you can repair a flat and be riding again in less than 10 minutes.
I would probably pick the nails up, and leave a sign saying, "Thanks for the nails. We needed them to fix our clubhouse. Let us know if we can ever return the favor".
Nothing takes the wind out of an insult better than the victim not accepting it as an insult. It drives the insulters crazy.......