The shop that painted my body (er, my Cobra's body that is
) coated the entire underside of the car with a chip-guard coating they use on the underside of street rod fenders. It's very similar to the bedliner material. It has a texture and is very hard.
In addition, I masked off and sprayed the areas in direct line with the tire treads with a soft undercoating to give some cushion in the event of a rock strike.
So far, I have no damage at all from stones.
Later,