Sunder Breaker

You place an invisible ward upon the target. The next time a creature succeeds at a sunder combat maneuver against the target, the attacker’s weapon takes 1d6 points of damage per caster level (maximum 10d6). If the attacker used a natural weapon for the sunder, the attacker takes half this damage. Spell resistance applies to this damage. The attacker can attempt a Fortitude save to halve this damage.

The ward on the target counts as a magical trap and can be detected and disabled as such.