Complete Warrior, page 66, PrC Occult Slayer, class ability Mind Over Magic: "Starting at 2nd level, an Occult Slayer can cause a spell or spell-like ability targeted against her to rebound onto the originator as a free action. This ability otherwise functions as the spell turning spell (caster level equals the character's Occult Slayer level + 5). An Occult Slayer can use this ability once per day at 2nd level and twice per day at 4th level."

Also, you should give the class Improved Buckler Defense (a feat from Complete Warrior, page 100) early on; it's not incredibly useful in the long run, but it does give a little more support to bucklers.