Seems like we've had this discussion before. I've suggested something before and I still think the best answer is to incorporate some type of challenge system, whereby, a higher rated player, if challenged, has to accept to play a game with a lower rated player (say up to a 200 point difference) at least once a month. If he/she does, thats fine. If he/she does not accept the game, then he/she forfeits the game. Note that he/she would only be required to play if challenged. If there are not challenges, then he/she doesn't have to play, and can keep her/his rating indefinitely and play with whomever he/she wants, no big deal. So if no one cares, then its no big deal and he/she can keep their rating as high as they have earned it as opposed to some rating degredation mechanism, which has so many problems and issues associated with it.

Also I think this would only apply to individuals rated in the top 10 or something like that. Its kind of like something we had on my high school chess team... (although I hate playing chess now... so slow)