Fortify Familiar

Universal
Level: Sorcerer 4, Wizard 4,
Components: V, S,
Casting Time: 1 action
Range: Touch
Target: Your familiar
Duration: 1 hour/level
Saving Throw: None (harmless)
Spell Resistance: Yes
Source: tome and Blood: A Guidebook to Wizards and Sorcerers

You make your familiar tougher.

While the spell lasts, it gains a +2 enhancement modifier to natural armor and has a 25% chance to avoid extra damage from sneak attacks or critical hits (though the attack still deals normal damage). The familiar also receives 2d8 temporary hit points.