  The current paper studies a protective mission to defend a domain called the
safe zone from a rogue drone invasion. We consider a one attacker and one
defender drone scenario where only a noisy observation of the attacker at every
time step is accessible to the defender. Directly applying strategies used in
existing problems such as pursuit-evasion games are shown to be insufficient
for our mission. We introduce a new concept of defense margin to complement an
existing strategy and construct a control strategy that successfully solves our
problem. We provide analytical proofs to point out the limitations of the
existing strategy and how our defense margin strategy can be used to enhance
performance. Simulation results show that our suggested strategy outperforms
that of the existing strategy at least by 36.0 percentage points in terms of
mission success.
