A few rock structures don't bother me, heck I've built a few small ones expecting they be toppled.  Nails I hate, hatchet hacks on trees I really hate, trash in fire pits I hate, but what really chaps MY ass, is profuse evidence that "the hand of man" has been wiping "the ass of man" strewn about the campsite.  On my last trip I found piles of feces and TP right next to tent sites. Some people are just pigs.