  We construct extensions of the Standard Model in which the gauge symmetries
and supersymmetry prevent the dangerously large effects that may potentially be
induced in a supersymmetric standard model by Planck scale physics. These
include baryon number violation, flavor changing neutral currents, the $\mu$
term, and masses for singlet or vector-like fields under the Standard Model
gauge group. For this purpose we introduce an extra non-anomalous $U(1)_\mu$
gauge group. Dynamical supersymmetry breaking in a secluded sector triggers the
breaking of the $U(1)_\mu$ and generates soft masses for the superpartners via
gauge mediation, with the scalars possibly receiving sizable contributions from
the $U(1)_\mu$ D-term. We find several classes of complete and calculable
models, in which the messengers do not present cosmological problems and
neutrino masses can also be accomodated. We derive the sparticle spectrum in
these models and study the phenomenological consequences. We give an exhaustive
list of the potential experimental signatures and discuss their observability
in the upcoming Tevatron runs. One class of models exhibits interesting new
discovery channels, namely $WW \not E_T$, $W\gamma \not E_T$ and $WZ \not E_T$,
which arise when the next-to-lightest supersymmetric particle is a short-lived
$SU(2)_W$ neutralino.
