A couple of years ago, I sprayed my wheelwells with Fusor Wheelhouse Coating; a black rubbery surface that absorbs the stone's impact (my car was really making a racket just going down the average street).
It can be painted (which I did) or left black, as is.
Unfortunately, my server has been down since the First of October (when my IT guy moved), so no pictures are immediately available.
Edit: product is Fusor 805 Wheelhouse coating, and I've applied it to the over fifty (>50) BMW M Coupes/Rdstrs that I've redone the weak trunkfloor/differential brackets on. With fine tuning the application gun, I can replicate the BMW factory undercoating almost perfectly.