If you want to make the game of ring toss really hard, use "coasters" instead of cut up spindle cover. Yet another use for the ubiquitous coaster.

Actually on second thought, maybe the person could leave the spindle cover intact, glue the base of the spindle to the top of the cover, then use the pointy bit of the spindle to stake it into the ground. Play "coaster golf" in the convenience of your own backyard...try to toss your coaster frisbees into the baskets created by the upside down cover shells.