Banner Woes

How awesome would it be if there was a banner item that decreased the damage it took from physical attacks. I mean.. If you're AP trying to hold lane.. AAing this beast for 3 minutes trying to kill it, meanwhile if you were to get a banner and fire it off the enemy (assuming AD champ) can kill it no problem. It's a downside to being a burst mage for sure but daaaaamn. Frustrating as hell!