Improved Uncanny Dodge (Ex)

At 5th level and higher, acan no longer be flanked. This defense denies a rogue the ability to sneak attack the barbarian by flanking her, unless the attacker has at least four more rogue levels than the target has barbarian levels.

If a character already has uncanny dodge from another class, the levels from the classes that grant uncanny dodge stack to determine the minimum rogue level required to flank the character.