Large and in Charge

STR 17+, Reach (Large size or larger),

When you make a successful attack of opportunity against an opponent who is moving inside your threatened area, you can force the opponent back to the square he was in before he provoked the attack. After you hit with your attack of opportunity, make an opposed Strength check against your opponent. You gain a +4 bonus for each size category larger than your opponent you are, and an additional +1 bonus for every 5 points of damage you dealt with your attack of opportunity. If you win the opposed check, your opponent is pushed back 5 feet into the square he just left.

When you make a successful attack of opportunity against an opponent who is moving inside your threatened area, you can force the opponent back to the square he was in before he provoked the attack. After you hit with your attack of opportunity, make an opposed Strength check against your opponent. You gain a +4 bonus for each size category larger than your opponent you are, and an additional +1 bonus for every 5 points of damage you dealt with your attack of opportunity. If you win the opposed check, your opponent is pushed back 5 feet into the square he just left.

You can prevent opponents from closing inside your reach.