Guardian

This special ability can only be placed on melee weapons. A guardian weapon allows the wielder to transfer some or all of the weapon's enhancement bonus to his saving throws as a bonus that stacks with all others. As a free action, the wielder chooses how to allocate the weapon's enhancement bonus at the start of his turn before using the weapon. The bonus on saving throws lasts until his next turn. Only the weapon's own enhancement bonus can be sacrificed, not any enhancement bonus provided by other effects such as a greater magic weapon spell. However, the total of such effects is still diminished by the amount allocated to improving saving throws.

If a weapon has both the defending and guardian abilities, allocating a single point of enhancement bonus increases either AC or saving throws, but not both.