if you use the right paper, like say for a heavy run start with 600 then work your way up to 2000. mask the area around the run just to keep from making a bigger repair spot than nessasary.wet sand it till its gone. slowly as not to go deeper than needed.TAKE YOUR TIME.then cut it with fine compound. if it shows when your done you may have to cut the hole fender. we have fixed a few that way and they turned out good. ken