Just found this description of the Leo Ring ong the Wikidot...
Perhaps when you used the Leo Ring you weren't using an appropriate weapon with it /shrug
- Does not affect critical hits (backstab & riposte: try the Hornet Ring) or striking a recoiling opponent (you have broken his guard, kicked him, or blocked his attack and caused him to stagger).
- To perform a counter, strike an opponent at the same time his attack
would have hit you or IMMEDIATELY afterwards, before they recover from
the "peak" of their attack animation.
- Normally this gives a ~20% physical damage bonus when using a weapon
that is capable of counter attacks. The Leo Ring boosts counter damage
by approximately 40%, for a total of ~67% greater power than normal.
- Counter attacks only give a bonus to physical damage, so the effect
is weaker with elemental, magic/enchanted, and divine/occult weapons.
The pure magic Moonlight Butterfly Horn cannot deal counter attacks at all.
- Confirmed counter attack weapons: Thrusting Swords, Spears, some Halberds (Scythe does not work but Lucerne and Gargoyle Halberd do, for example), Straight Swords and Katanas of all sizes that perform a thrusting power attack, Arrows
- The damage boost applies for almost every enemy in the game, including bosses and large foes.
Perhaps when you used the Leo Ring you weren't using an appropriate weapon with it /shrug