  The collective excitations of a zero-temperature, spin-polarized,
harmonically trapped, two-dimensional dipolar Fermi gas are examined within the
Thomas-Fermi von Weizs\"acker hydrodynamic theory. We focus on repulsive
interactions, and investigate the dependence of the excitation frequencies on
the strength of the dipolar interaction and particle number. We find that the
mode spectrum can be classified according to bulk modes, whose frequencies are
shifted upward as the interaction strength is increased, and an infinite ladder
of surface modes, whose frequencies are {\em independent} of the interactions
in the large particle limit. We argue quite generally that it is the {\em
local} character of the two-dimensional energy density which is responsible for
the insensitivity of surface excitations to the dipolar interaction strength,
and not the precise form of the equation of state. This property will not be
found for the collective excitations of harmonically trapped, dipolar Fermi
gases in one and three dimensions, where the energy density is manifestly
nonlocal.
