You should report this in the "typo collection" issue
And the harder it becomes to get them. But you can use "very aggressive" tactics to artificially lower your base DV and give the shield more chances of blocking attacks. Only Berserk prevents you from getting shield marks.
An entry in the the changelog for 0.9.9g14 says "Rings can be destroyed due to armor damaging hits in melee combat, although you wear gauntlets." I'm not sure if this is a bug being acknowledged as such, or an intentional effect.