  The dominant source of decoherence for an electron spin in a quantum dot is
the hyperfine interaction with the surrounding bath of nuclear spins. The
decoherence process may be slowed down by subjecting the electron spin to
suitable sequences of external control pulses. We investigate the performance
of a variety of dynamical decoupling protocols using exact numerical
simulation. Emphasis is given to realistic pulse delays and the long-time
limit, beyond the domain where available analytical approaches are guaranteed
to work. Our results show that both deterministic and randomized protocols are
capable to significantly prolong the electron coherence time, even when using
control pulse separations substantially larger than what expected from the {\em
upper cutoff} frequency of the coupling spectrum between the electron and the
nuclear spins. In a realistic parameter range, the {\em total width} of such a
coupling spectrum appears to be the physically relevant frequency scale
affecting the overall quality of the decoupling.
