Can we get an item with an armor aura (or active)?

I really like how Aegis and Locket passively give your team magic resist when you need it. But what if an AD champ is fed? It would be nice if we had ways of protecting our squishy champions from these threats. If you don't want to make it an aura that's fine. I guarantee you there are players who will remember to use the active. As far as how much armor it should give, I don't know. I'll let Riot figure out the numbers, but please give us a way of dealing with the numerous assassins running around.