Demolition

 
Prerequisite(s): Profession (siege engineer) 1+ ranks, Power Attack, Str 13+
 
Benefit: If you take a full-round action that provokes an attack of opportunity to strike an immobile, inanimate object, the strike is a critical hit and has it’s damage multiplied by your weapon’s critical hit multiple. You can only do this against an immobile object, thus it is not possible to score a critical hit against an object held or worn by another character this way. With this feat, it is also possible to score critical hits or do a coup-de-grace against constructs. These attacks are resolved in normal fashion except that constructs automatically pass their Fortitude saves against death when they suffer a coup-de grace.
 
Source: Mongoose Ultimate Feats