New Resolve Rune: Runic Shields
Cuz I liked that old rune. But it's new!!
Runic Shields: While you have a shield, you gain [100 - (600/600+Shield Size)]% damage reduction. You could put a little green tint around shielded champs with this rune just so people don't get confused.
Tweak the numbers how you like, but it would be a nice addition to have, and it would make something like Full AP Shen a complete bother.
Then on top of this, maybe we could add some items to deal with shields as well! Maybe some Lethality-AttackSpeed item that lets you deal (60% Lethality)% bonus physical damage to shields. You know, you can keep the ideas coming! It's more fun than just blurting out "WAH BROKEN!!!" like a complete monkey.