Daily Punch 9-4-14 Superior Shield of Fortification spell for Pathfinder

This is a spell I made up on the fly for the final of my Pathfinder Game.  I had a crit happy gunslinger, and I had to find a way to keep my big bad in the fight for more then five seconds.  This is the result

Shield of Fortification, Superior

School abjuration; Level cleric 7, inquisitor 6, paladin 6

DESCRIPTION

This spell functions as shield of fortification, except there is a 75% chance that the critical hit or sneak attack is negated and damage is instead be rolled normally, rather than 25%.

Thoughts?