I wrote a version of this in a thread in d20(RPG and General), and there are only minor changes. This is an attempt to give Fighters and the like a better chance against spells.
Shrug it off
Prerequisites:BAB + 11, INT 15, Combat Expertise, Great Fortitude
Benefits: Once per day (+ INT mod), you may use your fortitude save instead of a will save of a spell. You must declare the use of this skill prior to the roll.
