Idea to change Guardian

So, the current Guardian rune is a joke. One Q from Ezreal and it's gone for 45 seconds. Literally. That's actually dumb. It's like Yasuo's shield... but on a 45-second cooldown.

I'm thinking this should get reworked entirely. It wouldn't be hard.

Passive: If a nearby ally champion loses 50% of their health in under 2 seconds, gain 30% damage reduction and taunt nearby enemies for 0.25-1.5 seconds. Taunt duration increased for whomever dealt the most damage to that champion. 4-second cooldown, but 15-second cooldown per champion. Multiple champions cannot proc Guardian off of the same champion.

I don't know about the numbers. I just know it would be an amazing rune. Why? Well, a few reasons.

1. More incentive for the tank to actually stay near his allies.
2. It has great synergy with Font of Life (and Revitalise).
3. Its use is applied during combat instead of before combat, and it can't get negated by one pesky Ezreal Q. Unless one Ezreal Q does a shit-ton of damage.