You could always leave the core of the current system, but augment it by creating a 'minor shield', 'minor aura', 'minor barrier'. These wands could be ubiquitous, for sale throughout the world, but with a flaw. Their protection will only absorb a finite amount of damage before they crumble, and new protections cannot be reapplied until after the initial casting has worn off. If you wanted to make the minors less powerful, have a delay time between crumble and reuse even if they have not been fighting, like a crumble at 12 hours and 24 hour timer instead of 18 hour crumble and 24 hour timer.