The ability to guard items, exits, and or persons by physically blocking them. Maybe you're a bodyguard. Or you're trying to prevent someone from entering a room, or leaving a room for that matter. They have a chance at getting by, of course. A standard stealth vs. perception, or if that fails, strength(plus size/weight) vs. strength (plus size/weight).
It would also allow mobs to guard exits. Adding certain criteria would also be neat. Such as... If they're evil, try to prevent them from entering. Or if they're good. Of course, a spell that could mask alignment would also fall right into this...
