[Al Skierkiewicz]

The brake mode on a Victor simply puts an electrical short across the motor. (actually about .012 ohms) Any current generated by the motor is then shorted by this feature causing dynamic braking in the motor. Motors at high speed generate more current than a slow moving motor does, thus dynamic braking is greater at higher motor speeds. High gear ratio transmissions add to this effect.
There are a variety of ways to add a mechanical brake. Search other posts for "brake" and I am sure you will find some. Even a lowly servo can be used to engage a mechanical stop.