Constraining the structure and asymmetries within supernova (SN) ejecta is of great
importance to understanding the explosion mechanism and for constructing better
models of SN feedback mechanisms.  SN forbidden line profiles at later times, when
the ejecta is optically thin in the continuum, provide a potential diagnostic of
densities and the distribution of individual ionic species throughout the
proto-remnant. Further, asymmetries in the line shape can be used to understand
density and/or compositional inhomogeneities within the ejecta.  This is because in
forbidden lines,  the scaling of the emissivity with density changes at a
characteristic ``critical'' density that is set primarily by atomic constants.  As a
result, the evolution of total line flux has the potential to give a direct measure
of absolute density within the ejecta. We will present models of forbidden lines in
SN ejecta and examine the effect of local density variations (``clumps'') on their
profile shape, and examine how the total line flux varies with time in relation to
optical depth in the line and age of a SN.