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Two-headed (take ogre or giant) to reduce dual wielding penalties by 2
Two-weapon Style to make 4 attacks a round
Two-weapon Guard to treat the second shield's guard bonus as an insight bonus
Shield Supremacy to gain a additional +2 guard for each shield
Tower shields, both with Superior and Large-Scale and AP 2, one Giant-made and one Ogre-made
That's 4 attacks a round with a -3 to each attack, but doing 1d6+1+STR subdual damage every attack (and ignoring up to 2 DR), prompting a Fort save with each attack. Using the Shield Slam trick from Shield Mastery, if the target fails a save, he is also stunned for 1 round. Every attack with the Ogre shield prompt a Morale check and the Giant Shield has +2 threat against Medium or smaller targets. Oh, and gain a +10 to Defense.
Basically, pick one person and they have a very bad day.