Ring of Counterspell

This ring allows a single spell to be cast into it,
but that spell cannot be cast out of the ring again. Instead, should that spell ever be cast upon the wearer, the spell is immediately countered, as a counterspell action, requiring no action (or even knowledge) on the wearer’s part. Once so used,
the spell cast within the ring is gone. A new spell
(or the same one as before) may be placed into it
again.