Actually the brush type kick up WAY less crap than the more solid options! The best option IMO is mud flaps behind the tires and then Mr Sunshine covered the next layer of protection
Anything you put on near the rear bumper thinking protection that can EVER touch the road surface will kick up stuff! Think about how much rear travel your bumper sees when traveling down the highway and then how much more travel it will see on gravel roads. For some of us that bumper could only have a mini skirt and becomes sort of pointless