[llamabeast]

There are limits on the spells you can make to boost defense and protection. I don't think you actually can boost defense, apart from via quickness, and protection can either be barkskin, stoneskin or ironskin, nothing else. However you can couple these spells with appropriate elemental resists (again, most of them 100%) so that your troops don't get elemental weaknesses. For example the "resilience" spell in Tomb Kings is meant to make troops resistant to the danger and heat of the desert, and is Barkskin + Fire resist, which for some reason ends up giving them the protection bonus and 25% fire resist (not sure where the number 25 comes from).