I have a question for those who have placed caches. Do you really get landowner permission? If it's on City/State owned land, do you get permission from "Parks & Rec" or the park manager like you probably should?

This is one thing that has troubled me for awhile about this hobby. I don't want to be tromping around somewhere I'm not supposed to be. Nor do I want to be bothering/disturbing land and causing damage by being one of a hundred geocachers who go through to the cache.

I have a feeling that for the most part, people do not get permission from anyone to place a cache, and the thought of that bothers me for some reason. Maybe I am way wrong here, just an observation/question.