  Using data from the FOCUS (E831) experiment at Fermilab, we present a new
measurement of the branching ratio for the Cabibbo-favored decay mode $D^0 \to
K^-K^-K^+\pi^+$. From a sample of $143 \pm 19$ fully reconstructed $D^0 \to
K^-K^-K^+\pi^+$ events, we measure $\Gamma(D^0 \to K^-K^-K^+\pi^+)/\Gamma(D^0
\to K^-\pi^-\pi^+\pi^+) = 0.00257 \pm 0.00034(stat.) \pm 0.00024(syst.)$.
  A coherent amplitude analysis has been performed to determine the resonant
substructure of this decay mode. This analysis reveals a dominant contribution
from $\phi$ and $\bar K^{*0}(890)$ states.
