Ironskin

Your skin hardens and takes on the color and texture of rough iron. You gain a +4 enhancement bonus to your existing natural armor bonus (if you do not have a natural armor bonus, you are considered to have an effective natural armor bonus of +0). This enhancement bonus increases by 1 for every 4 caster levels above 4th, to a maximum of +7 at 15th level.

While you're under the effects of this spell, if an opponent confirms a critical hit or sneak attack against you with a physical weapon (not a spell or magical effect), you can dismiss this spell to negate the critical hit or sneak attack and treat it is as a normal hit. Dismissing the spell in this way is not an action, but you must be conscious and aware of the attack to do so.