[Sam]

If you have the siege weapons for offense, (battering rams and ladders) why not ones for defense? I'm talking boiling oil or big rocks. Things like that.

Maybe you could also make so the more battles you are in the more skill you get. Like if someone keeps attacking you, you'd learn their attack pattern and get a defense boost?

And for spells, maybe spells that affect attack conditions. Like having your mage cast a big old fog spell, so your troops could sneak in unseen and give you an attack bonus.