You say what rules?
See the Geocaching Guidelines at this link:
http://www.geocaching.com/about/guidelines.aspx
PART OF IT IS SHOWN BELOW:
Off-limit (Physical) Caches
By submitting a cache listing, you assure us that you have adequate permission to hide your cache in the selected location. However, if we see a cache description that mentions ignoring "No Trespassing" signs (or any other obvious issues), your listing may be immediately archived.
Caches may be quickly archived if we see the following (which is not inclusive):
Caches on land maintained by the U.S. National Park Service or U.S. Fish and Wildlife Service (National Wildlife Refuges)
Caches that are buried. If a shovel, trowel or other “pointy” object is used to dig, whether in order to hide or to find the cache, then it is not appropriate.
Caches that deface public or private property, whether a natural or man-made object, in order to provide a clue or a logging method.
Caches placed on archaeological or historical sites. In most cases these areas are highly sensitive to the extra traffic that would be caused by vehicles and humans.
Caches hidden in close proximity to active railroad tracks. In general we use a distance of 150 ft but your local area’s trespassing laws may be different. All local laws apply.
Caches near or on military installations.
Caches near or under public structures deemed potential or possible targets for terrorist attacks. These include but are not limited to highway bridges, dams, government buildings, elementary and secondary schools, and airports.