replace bond of stone

I actually use bond of stone when I go tank support with these guys:

Grasp isn't that bad if you proc it often.

Bond of Stone is pretty meh, especially since Knight's Vow does the same thing, but better. The damage transfer and damage reduction is hardly noticeable, nor do I believe it gives much invisible power.

What if there was a mastery along the lines of the longer a champion stays in battle, the more % damage reduction that champion gains. Every second grants 2% reduction up to 12% (just throwing a percent here, I'm no game balancer). There must be an enemy champion within 600 units to retain this effect.

Now this is an interactive keystone, while not being too overbearing like CoC. It's power will not be very obvious, similar to BoS, but at least this one isn't garbage.