For all the misery the ring caused, they could've smithed a large iron ring through the center and strap it onto someone's back, and there would've been no problem.
Taking an invisible dump is a close second tho.
Discussion
But the poop would pass through the ring, rendering it invisible only until it passed through then becoming visible again as it dropped to the ground. Shitty parlor trick. Then the poop stuck to the inside of the ring would remain invisible until you put the ring back on. Not a great situation.