Ring of counterspells

This ring might seem to be a ring of spell storing upon first examination. However, spells cast into the ring cannot be cast out of it again. Instead, should such a 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, and the ring’s spell storage capacity freed up accordingly.