By powerful I mean the ability to sustain an injury to it's lowest level for instance be able to use strength against a wrong move.
AH! Resisting against the wrong move WILL create injury.
The way to avoid injury is to relax and move INTO the "wrong move" until you can escape or take a fall/roll.
Also you can INSIST the younger students SLOW DOWN so that if they "crank" hard on your joints you have time to tap out.