Originally Posted by martianone
make sure the stoker has some eye protection,
dust and stones seemed to target the back.
Zefal makes (or used to) a short fender that straps to the downtube. I used one on our Trail-a-bike to deflect anything from the rear tire. It was small enough that I could leave it in place even when folding the bike, but still big enough to keep stuff out of his face.