this is what i do, but be fucking careful when messing with your bindings.
when they fall off waaaay too easy tighten up your forward pressure a click or two. (its the screw on the heelpiece that when you turn it the heelpiece slides forward)
if they fall off again, and you feel like they should have stayed on tighten up your din settings on the toe and heel pieces.
eventually you should get them to a place that when they come off you feel as if they actually needed to release. also, periodically your bindings can "loosen" a little bit, and even though you've cranked 'em down, you may need to tighten them a little more. good luck, and be careful dude. blown knees suck.