If you have a snap closure that tends to come un-snapped, you can place the male end of the snap on a vise or anvil, and gently peen the top of it. This will enlarge the circumferance of the snap button and it will seat much tighter in the female side.
First thing I do to a pair of boxer shorts is peen the snap so whenever I bend over at the waste, my belly doesn't cause my boxers to come un-snaped. Works on boat covers too.