In this work, we propose a modified DEFENSE architecture termed as xDEFENSE that can detect and react to hardware attacks in real-time. In the past, several Root of Trust architectures such as DEFENSE and RETC have been proposed to foil attempts by hardware Trojans to leak sensitive information. In a typical Root of Trust architecture scenario, hardware is allowed to access the memory only by responding properly to a challenge requested by the memory guard. However in a recent effort, we observed that these architectures can in fact be susceptible to a variety of threats ranging from denial of service attacks, privilege escalation to information leakage, by injecting a Trojan into the Root of Trust modules such as memory guards and authorized hardware. In our work, we propose a security monitor that monitors all transactions between the authorized hardware, memory guard and memory. It also authenticates these components through the use of Hashed Message Authentication Codes (HMAC) to detect any invalid memory access or denial of service attack by disrupting the challenge-response pairs. The proposed xDEFENSE architecture was implemented on a Xilinx SPARTAN 3 FPGA evaluation board and our results indicate that xDEFENSE requires 143 additional slices as compared to DEFENSE and incurs a monitoring latency of 22ns.