Asymmetric threats in the current world are focused on various critical infrastructures. We choose a subset of the infrastructures and a set of surveillance policies, and we propose a number of security countermeasures that should be able to detect and potentially prevent a potential attack. Our goal is to provide a unified decision support platform ARETHUS to help decision-makers notice a threat and then choose from a computed array of potential preventive actions. The platform is built using a mixed-reality concept, and allows mixing of real-world and simulated data to provide not only a real-time work environment, but also a testbed to test out various scenarios. We plug in a number of algorithms computing various patrolling policies for heterogeneous agents, and we make the platform extensible for use by others. We demonstrate the usability of the platform and the performance of the algorithms on a set of pipeline protection scenarios.