zipper?

[weeefairy.livejournal.com]

sorry about the question only post,

but ive had a problem lately with the zippers of both the pairs of pants i own (i usually wear skirts xD) they just keep coming undone!
no matter what i do, they just keep opening on me,
i know i can hook up a safety pin to it, but isnt there a more uhm, permanent, more practical thing i can do?
or can i basicly just throw them away?

--edit--

do you think slightly filing the metal pieces of the zipper would work?