do your fog lights have 9145 (stock wattage) bulbs or the 9005's?
I ask, because when i had the 9005's in my fogs, they too would get s chip in them, then the whole lens would break. after i went back to using 9145's, the lights never cracked or broke again. (i guess the heat breaks the glass)
unfortuately, there are no covers for these fog lights.