Rose hips are selling for some sort of astronomical figure in the health food store here..something like $80 a pound or something.. even if they are dried that seems like pretty high cost goat feed
Maybe try cutting it back very severely and then heavilly mulching with cardboard and then sawdust or some such to hold the cardboard in place, from the base of whatever plants you are leaving to at least a foot past the remaining stubs. Or cut it way back and turn pigs in there and see if they will root out the roots for you.
I think, and if I'm wrong someone will be quick to point it out:) that if you keep any green plant from light and water long enough it will soon start to struggle. (Seeds are a different story).