I recently went on holiday to Centre Parcs and am still in the facebook group for that particular location. I've seen numerous posts from people about to arrive, showing off the 100+ painted rocks they have prepared and will be hiding around the park during their holiday.
We didn't have room in our car for a spare gnats nadger, I can't imagine the look on DHs face if I went "ah, just the rocks to squeeze in".
I guess on the positive, it's a free activity for others to do at CP, where it feels like if they could charge you for farting whilst on the park they would. And it doesn't do anyone any harm. But I just don't understand the compulsion to paint hundreds of rocks and hide them around. I can be a miserable c**t though, so maybe it's that!