Random Magic Armor (any level)

This suit of armor or shield produces a magical force that protects vital areas of the wearer more effectively. When a critical hit or sneak attack is scored on the wearer, there is a chance that the critical hit or sneak attack is negated and damage is instead rolled normally:

Aura: Strong abjuration
Caster Level: 13th
Requirements: Craft Magic Arms and Armor, Limited Wish or Miracle
Price: varies (see above).
Source: Dungeon Master's Guide v.3.5