Before I bought mine, I wasn't sure how available they were.
So, to stop rocks and water from getting into my bumper and potentially ruining my fog light, I took the lid from a plastic box (I'm not sure on their true name??) and cut a square out of it. Then I spray painted it black, got some double sided 3M tape and stuck it on the fender wall. Then I ran black Electrical tape around the side of the square just in case. It works pretty well.

I wasn't sure what those plastic containers were called, but everyone has em. They look something like this:
http://image.made-in-china.com/2f0j0...SL-069102-.jpg