+1 for the flaps. One on the rear as well if you're riding in groups. I still feel the sting of being told I couldn't ride with the fast boys group until I had a flap on the back...

I used to cut a water bottle as in my pic, but I've been using stair tread liner from the hardware store and it's better looking and able to be shaped perfectly. I run em as low as they'll go and use zap straps, and sometimes some adhesive, to hold 'em on.