  We develop a theory for the spin-echo dynamics of a heavy hole in a quantum
dot, accounting for both hyperfine- and electric-field-induced fluctuations. We
show that a moderate applied magnetic field can drive this system to a
motional-averaging regime, making the hyperfine interaction ineffective as a
decoherence source. Furthermore, we show that decay of the spin-echo envelope
is highly sensitive to the geometry. In particular, we find a specific choice
of initialization and {\pi}-pulse axes which can be used to study intrinsic
hyperfine-induced hole-spin dynamics, even in systems with substantial
electric-field-induced dephasing. These results point the way to designed
hole-spin qubits as a robust and long-lived alternative to electron spins.
