Pick two holidays roughly six months apart--say St. Patricks Day and Labor Day--and on those dates use the cans to fill your cars. If you can't rotate all your stock at once, refill the ones you do use, and turn them so the lid faces the direction opposite of the ones that still need to be used, and continue to top off your car, until the rotation is complete. I picked St. Pat's and Labor Day, because those are always good days to get "gassed." ;-) There's your mnemonic to remember to do it!