I really like the way you are headed in this (Defensive Skills).
What SHOULD happen:
1st: Minecraft stops making it so swords block, and give a shield-like item.
If you hit the shift key with the shield in your inventory, it would block an attack a certain percent (Projectile or Fist/Swords)
After a lot if hits, it would wear out... It could be made by using different types of ingots for different amounts of protection...
It just feels weird with a sword, but yeah sorry for getting off track.