If you use aquarium silicone adhesive, they won't be damaged, the adhesive is weather proof, and the silicone gives a flex and wiggle that prevents sheering. We had a dime stuck to our porch for 8 years and when it finally came up, it was because the concrete had eroded underneath it.

My dad taught that one to me in high school. He stuck $1.50 in random change to the ground in front of the soda machine at the apartments he was groundskeeper for. On slow days he'd sit and watch the local kids try desperately to get a free soda with money they can't pick up.

Nailed? Glue might be better. Like a gorilla glue or epoxy resin.

Salesmen at a local car dealership would super glue quarters to the parking lot. The porters and/or customers would always try to pick them up, and it brought us so much joy to watch.

Glue the finger rock to the ground, got it.