I'm curious; two-weapon defense says that it requires you to be wielding two weapons, and doesn't work unarmed or with natural weapons. However, shields do appear on the list of martial weapons, they're in the Close Weapons group for Fighters, and you can use Two-Weapon Fighting with a shield, so...it seems like this would work. Combined with Shield focus, you could get as much as +4AC from your shield, unless Shield bonuses don't stack.
|B. A. Robards-Debardot|
So, it might work like this:
If you use your shield as a weapon, you lose the AC to it. BUT since you don't have a shield AC, Two Weapon Defense could now kick in.
I don't know WHY you would do it, but it should work.
Maybe if you were TWF with two shields? If you decide to get Shield Master, shields are probably the best weapons for you to TWF with.
|James Risner Owner - D20 Hobbies|