Just make strength the difficulty of shields like melee weapons. Why do you need to be agile to use a huscarl or board shield? Why are shields the only equipment (besides horses) in which the difficulty is derived from agility and not strength? All it does it make shielders a ridiculous agi class. Bucklers and smaller shields are for high shield skill and agility, board shields, kites, and huscarls are for non-skilled utility. Make slight stat and price adjustments accordingly.