Aside from the difficulty to make them, a power source or some thing would likely be necessary for continued use. Spells and enchantments are set up to have a certain draw of power when activated. And continuous use of said spell or enchantment would require a power source. Runes are a one time thing, requiring magic at their activation before the effect is finished. As well, a question to all of the staff is likely in order for making automatons of any variety.