I used JB Weld on some snaps for my jango Knees. So the femail part of the snap is JB Quik Weld'd in place and the male sides are puched into the elastic with it doubled over on the ends to leave room for you to pinch the elastic and pull upon removal. That way it gives you something sturdy and a little more durable to grab onto on the end of the elastic where the snap is..
I hot glued 2 of those cloth coated elastic hair ties. Cheap as hell, pretty durable. And if you ask your sis/gf/mom/whatever for a couple, odds are you can get some fo free! (unless she's a *****, or doesnt have any or something)
Tempted to add a lil square of velcro above the knee though, just in case.