I would say use of shields is covered as much as the use of knives or swords or axes are under the Weapon skill. Nitpicky of me probably, but most shields (until hou get to tower shields and pavis) are not armor...they are weapons. Defensive weapons, but still weapons. Much like a main gauche. Tower Shields are more like portable cover than armor or a weapon....unless you have Inhuman or higher Strength.

I would give a bonus to Defense and to Damage as the base ability for a shield. A Stunt Tree for shields would be nice though.

-Weylin