  We derive an effective Hamiltonian for a (001)-confined quasi-two-dimensional
hole gas in a strained zincblende semiconductor heterostructure including both
Rashba and Dresselhaus spin-orbit coupling. In the presence of uniaxial strain
along the $\left\langle110\right\rangle$ axes, we find a conserved spin
quantity in the vicinity of the Fermi contours in the lowest valence subband.
In contrast to previous works, this quantity meets realistic requirements for
the Luttinger parameters. For more restrictive conditions, we even find a
conserved spin quantity for vanishing strain, restricted to the vicinity of the
Fermi surface.
