Garden hose would burn them worse than a cotton rope.. I would rather a soft cotton rope give me a rope burn than a rubber hose that pulls my skin and hair off with it at once..
I agree with the posted above that said a portable fencing system.. for a horse to learn where a rope is, its gotta be burned with it-- why do that to them? Why not just tye the horse to a highline picket, with a hay net?
You ever been around a horse that's been rope burned?.. they become scared of ropes, or anything that resembles a rope-- and there is a lot of re-training involved.. I suggest finding a trainer whos experienced to help you with this. :)