  In this paper, we consider the problem of protecting a high-value unit from
inadvertent attack by a group of agents using defending robots. Specifically,
we develop a control strategy for the defending agents that we call "dog
robots" to prevent a flock of "sheep agents" from breaching a protected zone.
We take recourse to control barrier functions to pose this problem and exploit
the interaction dynamics between the sheep and dogs to find dogs' velocities
that result in the sheep getting repelled from the zone. We solve a QP
reactively that incorporates the defending constraints to compute the desired
velocities for all dogs. Owing to this, our proposed framework is composable
\textit{i.e.} it allows for simultaneous inclusion of multiple protected zones
in the constraints on dog robots' velocities. We provide a theoretical proof of
feasibility of our strategy for the one dog/one sheep case. Additionally, we
provide empirical results of two dogs defending the protected zone from upto
ten sheep averaged over a hundred simulations and report high success rates. We
also demonstrate this algorithm experimentally on non-holonomic robots. Videos
of these results are available at https://tinyurl.com/4dj2kjwx.
