Place sharpshooters. They do the most damage with they crits passive.
I did not understand what this would be
Sharpshooters, the one with long rifles. You place them on wall defence, they have passive skill, that makes they attacks criticalm mostly lethal for units and heroes.
They are best for walls defending, if you use dwarfs.
For the front line defence, you can use mechs and tanks, if you have a lot of resources, because they can die(not just injured).
Another type of dwarf units will be wiped out fast from the defence if the attacker has equal or more power.