Magic:Stone Bones

Transmutation
Level: Clr 2, Sor/Wiz 2
Innate Level: 2
Component(s): V, S
Casting Time: 1 action
Range: Touch
Target: One undead creature
Duration: 10 turns/level
Counter(s): --
Saving Throw: None
Spell Resistance: No
Metamagic: Extend, Quicken, Silent, Still
Energy Substitution: No

You cause the target undead to gain a +3 natural AC bonus, due to the thickening of its bones.

Alternatively, Transmutant Mages casting this spell turn the targeted undead into a Risen Lord for 1 round per 2 caster levels; this destroys the undead after the spell expires.