Excellent reply by HIPS-meister. As an example of a cache that was the result of a compromise with park authorities, check out Fort Yargo geocache. Georgia state park policy prohibits the placement of cache containers, so a very clever scheme was devised with the co-operation of the park manager at this park. The cache is a multi-stage where you travel around the park collecting numbers. Those numbers are then combined to form the combination for a padlock that is on the cache container. The container itself is obtained from a park employee at the end of your search, but of course you need the combination to be able to open it. I thought this was a very clever way to work around the restriction and still provide a fun and interesting "hunt".
Unfortunately the cache is currently unavailable, but that is merely a technical matter.