I used this bumper
57010 - TBR 1/8 NM2 Rear Bumper - Tekno ET48

bolted to this wheelie bar
96027 - T-Bone 1/8 Truggy Wheelie Bar (Y129)

(sorry, too new to post links)

I zip tied the Tbone bumper to the stock bumper.
It provides more protection than the stock set up and there's a wheelie bar, but it would be nicer to have more protection still. I would like to see a bumper that goes up further and cover the back of the body.