Improved Uncanny Dodge (Ex)
At 5th level, a barbarian can no longer be flanked. This defense denies enemies the ability to sneak attack the barbarian by flanking her, unless the attacker has at least 4 more levels in a class that provides sneak attack than the barbarian has barbarian levels. If the barbarian also has uncanny dodge from another class, levels from the classes that grant uncanny dodge stack to determine the minimum level required to flank the barbarian.