The Sliding-singlet Mechanism Revived

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.