The increased capabilities of modern real-Time systems (RTS) expose them to various security threats. Recently, frameworks that integrate security tasks without perturbing the real-Time tasks have been proposed, but they only target single core systems. However, modern RTS are migrating towards multicore platforms. This makes the problem of integrating security mechanisms more complex, as designers now have multiple choices for where to allocate the security tasks. In this paper we propose HYDRA, a design space exploration algorithm that finds an allocation of security tasks for multicore RTS using the concept of opportunistic execution. HYDRA allows security tasks to operate with existing real-Time tasks without perturbing system parameters or normal execution patterns, while still meeting the desired monitoring frequency for intrusion detection. Our evaluation uses a representative real-Time control system (along with synthetic task sets for a broader exploration) to illustrate the efficacy of HYDRA.