Stone damage to my Vibe

[Rico Rose]

The weather cleared enough for me to give my Vibe a good cleaning and wax job. When I got to the rear wheel flairs ( I have the base two tone) I noticed that there were many pocks and pitts on them due to stones/salt. I plan on installing mud flaps soon (wish I would have done it before last winter) but the damage is done. How can I get these marks off the plastic? I was wondering if they can be sanded with a fine grit block or paper...