Clockwork Sword

When a creature you can touch is attacked by a hostile creature, you can cast Clockwork Sword to protect the target until the end of your next turn, or until the spell has been triggered. If the spell has not been triggered by the end of the casters next turn the spell dissipates. The targets AC now has a bonus of 1 + Spell level expended. 

At Higher Levels. Starting at a 3rd level Spell, if the hostile creature misses the attack they take 1d10 of slashing damage from the Clockwork Sword with an additional 1d10 per Spell level expended.