Most of the racers who ride fixed on the road use a front brake only. Keep in mind that no matter how much you think you will use the brake, your legs will take the first hit of a slow down. The instinct to any slowing is to stop pedaling and brake. At the track, we do drills where we practice slowing rapidly by using our legs but we do not do this too much. The track offers the perfect venue for fixed gear due to the banking. One can always go up track and kill speed and there is the apron where we can exit and slow down over a long distance.