  It is shown, using a modification of an idea of Sen, that completely
realistic supersymmetric grand-unified theories based on SU(6) or larger
unitary groups can be constructed using the sliding-singlet mechanism. These
models have a simple structure, preserve the successful prediction of $\sin^2
\theta_W$, and can suppress Higgsino-mediated proton decay to an acceptable
level in a simple way.
