My bad your absolutely right. Something that worked good was the old chicken wire basket stretchers. Strap patient down, then strap basket stretcher over patient. They were going no where. Of course hard to take vitals and all but....
Actually though proper use of triangle bandages, backboard straps, c-collars, spit sock, chemicals, and regular belts you should be able to safely restrain a person. If not have the cops shoot them, then treat for lead poisoning.