Generic SO(10) GUT models suffer from the problem that Planck scale induced non-renormalizable proton decay operators require extreme suppression of their couplings to be compatible with present experimental upper limits. One way to resolve this problem is to supplement SO(10) by simple gauged discrete symmetries which can also simultaneously suppress the renormalizable R-parity violating interactions when they occur and make the theory "more natural". We then present an extended 16 H model, with three 10 and three 45-Higgs, which is free of this problem. We propose this as a realistic and "natural" model for fermion unification and discuss the phenomenology of this model e.g. its predictions for neutrino mixings and lepton flavor violation.