The "Shields Shall Be Splintered" rules by Brian Murphy are popular amongst OSR bloggers. Basically the player's shield is splintered apart in battle before they are defeated. A nice simple rule that provides for more character longevity... but really one that's more cinematic than historic in origin.
Here's some footage of the Samurai Kanabō a weapon designed for breaking armour being used against a Viking Shield and a Spartan Shield with the user going all out trying to break the shields.
This is why I don't use the Shields Shall Be Splintered rules in my own games. :)
Go to 05:55 in the video to see the part about Shields.