Well, to be perfectly honest, I sort of like avenging charge, but not most of the other suggested changes. Cutting the AC bonuses kills half the point—making yourself unhittable at the expense of mobility. Without copious AC boosts, you're not really a very good wall. I can see reducing them and switching part over to CMD, but not eliminating them.

The maneuver progression is mostly from DS (every other level, with one readied every 3); I added 2 stances but I can cut it back to one and reduce the number readied if that seems more balanced.

The save type change was because resistance bonuses are common as dirt, and the DD +2 would probably not matter by level 8 (maybe you'd only have a ring +1, but you'd get a better one pretty soon).

I sort of liked the mobility abilities (passwall and dragon's tooth), but they're not defender-y enough. I could see them, but I didn't want to sacrifice anything to get them, and leaving them in made it way too full.

It essentially has the DS skill list. Balance is Acrobatics, Concentration/Listen/Spot are rolled into Perception (Concentration only for purposes of Diamond Mind; for casters it's a level check now), Craft stays, Intimidate stays, Knowledge goes because it's a powerful enough PrC with a limited skill list. Martial Lore is pretty useless, and since I'm designing this for a game that does not include it, I left it out.

Avenging charge is quite powerful for an at-will ability that doesn't end your stances. I would perhaps suggest making it recharge as though it were a martial maneuver and force you to sacrifice the mountain fortress stance (but not defensive stance).

Making this available at level 5 is WAY too powerful, especially with Mountain Fortress at level 1. DS was a little weak as published, but not extraordinarily so; moving its signature ability down 5 character levels is obscene. I nerfed the stance from DD to make it available more often (DS mechanic), but moving it down 2 more levels is still too good.