Currently, if I'm not mistaken, brick walls have the most durability and are therefore the strongest walls you can build. I don't mind brick walls being in the game, but I do not think they should be the strongest walls you could build.
I think the strongest, and final walls you build should be something more "dwarven". May I suggest something like "Runed stone walls"? They would be stone bricks that have mithril dwarven runes carved into them making them magical. You could craft them using stone and maybe one mithril ore or ingot. Maybe they could even damage the enemies that attack it, like when they attack the wooden spikes.
Thanks for your time!