Replace an action in your system with an action of the opposite sort.

Illustration:

As ballast for the bathyscaph (a navigable ocean-diving vessel designed to reach great depths), inventor Auguste Piccard placed steel shot in steel containers fitted with electromagnetic valves. Each valve consisted of a cylindrical pipe around which an electric magnet was wound. When current was flowing, the shot coalesced and acted as a reliable plug. By varying the current, the shot discharge could be precisely controlled. If the current was interrupted for some reason, the shot was discharged and the bathyscaph surfaced.

As an emergency provision, the shot containers were held in place by electromagnets, which discharged from the bathyscaph if current was interrupted. These electromagnets were continually charged by a battery. If all jettison devices failed, the charge died out within 16 hours, the containers separated from the bathyscaph, and the bathyscaph surfaced.