The Apollo landing sites should be preserved forever as milestones in human history, but there's technically nothing to prevent someone from going up and mucking around with them (the only thing forbidden is actually taking the hardware, which remains U.S. government property).
NASA is working on it. In this article, Leonard David describes how the space agency has drafted guidelines to protect sites of manned and robotic lunar exploration. NASA would prohibit any unofficial visits to the two most significant sites - Apollo 11 and Apollo 17 - and limitations on human or robotic visits (like those of Google Lunar X-Prize landers) - to the other locations.
COMMENT: We don't think nearly often enough about how to maintain what we're doing here and now as a record of future generations to understand what we were like and why we valued the things we did. This is an important first step.