  The Ultra Compact Dwarf (UCD) galaxies recently discovered in the Fornax and
Virgo clusters exhibit structural similarity to the dense nuclei of nucleated
dEs indicating that the progenitor galaxy and its halo have been entirely
tidally disrupted. Using high resolution $N$-body simulations with up to ten
million particles we investigate the evolution and tidal stripping of
substructure halos orbiting within a host potential. We find that complete
disruption of satellite halos modeled following the NFW density profile occurs
only for very low values of concentration in disagreement with the theoretical
predictions of CDM models. This discrepancy is further exacerbated when we
include the effect of baryons since disk formation increases the central
density.
