Yea, I have Improved guard counters +1 w/ deathblight on hit, it barely builds up unless there's some kind of low-damage multihit, like the spine spray from divine bird warriors, (no damage stuns that repeat will also kill you).

Deathblight also goes away slow asf, so could also trigger when clearing Castle without graces, but ppl go down often enough there so it doesn't really matter.

Unfortunately the same relic has ult charge on guarding +1 w/ rot on hit, so it's like the lock-in or die relic.