The Shield Master (3.5 Base Class, PEACH)

[Yitzi]

Well, alright. What do you suggest for a DR progression then?

I'd say allow him to turn points of shield AC into DR at a 2-for-1 rate (or 3-for-1 if you're looking for a powerful class), up to a maximum DR equal to his class level. Maybe make it not work when he loses his DEX bonus to AC, so as to give another way to get around it.

Well, my game is 3.5, this class is 3.5, Sunder doesn't happen in 3.5.

3.5 doesn't have a class known as the Shield Master. Whenever you homebrew, you are implicitly changing the rules to some extent.

And what happens if you are in a group without a person who can cast mending or repair? Not every group has a caster, not every campaign has magic period.

In a magicless campaign, that is more of an issue, but even so, it can be made into a new use for the Craft skill.

Your solution is probably "Hire someone to cast it". That would require the entire group turning around and heading back to nearest city, interrupting whatever quest they were on, and the whole way back, the fighter or shield master is useless in combat.

No; he can easily have a backup. It wouldn't be enchanted, so it's not something he'd want to use long-term, but just until he gets a chance to fix his main one it could be ok.