My understanding is Blizzard plans to keep the details of the math secret because they don't want the system to be gamed. Considering how seriously people take

My understanding is Blizzard plans to keep the details of the math secret because they don't want the system to be gamed. Considering how seriously people take SC2 I can hardly blame them for this decision. This raises the question of what it would take to create a ranking system that wasn't susceptible to active "attack" by people trying to game the system. One aspect of SC2's ranking system that doesn't seem to exist is some sort of skill decay. I used to be a Diamond level player but I haven't played seriously in months. Yet, my rating is still high as if I was that good. It seems like my only option is to log in and get destroyed for a few days to have my rating drop, which is not really something I want to do.