Life Shield

Conjuration (Healing)
Level: Artificer * 3, Cleric */Oracle * 3, Druid * 3, Hunter * 3, Paladin * 2
Components: S, DF
Casting Time: 1 Standard Action
Range: personal
Target: you
Duration: 1 minute/level or until discharged
Saving Throw: -
Spell Resistance: -
  You surround yourself with a positive energy field that damages undead opponents. Each time an undead creature damages you with a Melee Attack, that creature takes an amount of positive energy damage equal to half the damage it dealt to you. This damage is calculated after applying your Damage Reduction, resistances, and other defenses. Once this spell has dealt 5 points of damage per Caster Level (maximum 50), it is discharged.