I think a great defense addition would be a series of upgradeable towers you can add to your walls. Similar to the Archer towers... but you can chose which troops (trained at barracks) to deploy inside, who can die and need replenished after attacks.
Upgrades would include different skins to show higher levels, more troop capacity, and increasing range of aggro.... ie: lvl 1 has 1 housing space, 5 tile aggro
at the moment, the attack defense balance isn't perfect. attacks often win
bu this would completely flip it around, and no-one would win attacks against active people
