The imposed communication network brings more vulnerabilities to the evolving smart grid. Therefore, defensive techniques such as intrusion detection will need to be deployed in this already complicated system. Deployment and runtime cost due to the defensive trust systems will affect the original function of smart grid system without careful planning and design. This paper is an effort to address this important issue. In particular, the set packing algorithm is used to optimize the placement of the trust nodes of the defensive system in the multiple layer architecture of the smart grid. After the trust nodes are placed, a trust node aware optimal routing algorithm is used to find the least cost routing in the communications of the nodes. Also, an algorithm to identify new trust node(s) is presented to address the fault tolerance requirement of the smart grid system. Simulation results demonstrate that our approach is promising by providing secure, efficient, and reliable communications in the smart grid network.