Legendary Toughness

 
Prerequisite(s): Con 13+, Base Attack bonus 12+, Great Fortitude, Toughness
 
Benefit: You gain damage reduction 1/-, allowing you to negate the first point of damage that you suffer every time that you take hit point damage. This can reduce the amount of damage that you suffer to 0 but never below 0. This feat can only be taken once and stacks with all other feats and abilities that provide damage reduction.
 
Source: Mongoose Ultimate Feats