“What do you think his punishment should be for putting a rock into a place where nature was destined to put it?”
Put it back. As it was.
I could go along with that, although the value of doing so is probably much, much less than the cost.
Also, if that rock later on DID harm somebody, I would expect the government to pay dearly for having not only tolerated such a dangerous situation but for having caused it to be re-created.