Stone Bones

(Spell Compendium, page 208, DnD 3.5)

Transmutation

Level: ; Cleric 2; Sorcerer/Wizard 2
Components: V, S
Casting Time: 1 standard action
Range: Touch
Target: Corporeal undead creature touched
Duration: 10 minutes/level
Saving Throw: Will negates (harmless)
Spell Resistance: Yes (harmless)

A brief flash engulfs your ally, and through his flesh you can see his skeleton. The skeleton glows a foggy gray for a moment, thickening with eldritch power, then all is as it was before.

You cause the skeleton of the target corporeal undead to become thicker and as strong as stone. This gives the subject a +3 enhancement bonus to its existing natural armor.

Arcane Focus: A miniature skull carved of granite.