Thought about it some more and I think 90 days should start the decay process and it then continues each 30 days ... and percentages are a better option.

If someone is playing, and they are "bottom feeders" (never heard the term before but I think its great!!!!) then so be it ... they eventually plateau anyway and how interesting can they be! For those who use programs, variants often sort them out as only rudimentary programs exist for things like atomic chess and I have never heard of a game engine for tablut or tank battles. Looks like I am saved from fritz (but not myself :)