  We study the decay of $D^0$ and $D^+_s$ mesons into five-body final states
including a $K_S^0$ and report the discovery of the decay mode $D_s^+\to K_S^0
K_S^0\pi^+\pi^+\pi^-$. The branching ratio for the new mode is
{${\Gamma(D_s^+\to K_S^0K_S^0\pi^+\pi^-\pi^+)} \over {\Gamma(D_s^+\to
K_S^0K^-\pi^+\pi^+)}$} = 0.102$\pm0.029\pm$0.029.
  We also determine the branching ratio of {${\Gamma(D^0\to
K_S^0\pi^+\pi^+\pi^-\pi^-)} \over {\Gamma(D^0 \to K_S^0\pi^+\pi^-)}$} =
0.095$\pm0.005\pm$0.007 as well as an upper limit for {${\Gamma(D^0\to
K_S^0K^-\pi^+\pi^+\pi^-)} \over {\Gamma(D^0\to K_S^0\pi^+\pi^+\pi^-\pi^-)}$}
$<$ 0.054 (90% CL). An analysis of the resonant substructure for $D^0 \to
K_S^0\pi^+\pi^+\pi^-\pi^-$ is also performed.
