  We propose a mechanism for sufficient suppression of dimension-5 operators
for proton decay in a supersymmetric SO(10) model. This mechanism is analogue
to the double seesaw mechanism in studying neutrino masses. Only an
intermediate VEV instead of an intermediate scale is required so that gauge
coupling unification is maintained. The VEV is generated by introducing an
anomalous U(1) symmetry whose breaking is at higher scale. The proton decay
amplitudes are suppressed by this VEV over the GUT scale. We use
$\textbf{45+54}$ in breaking GUT symmetry. $\textbf{120}$ is included so that
fermion sector is fully realistic. Assuming a minimal fine-tuning in the Higgs
doublet sector, $\textrm{tan}\beta$ of order one is predicted.
