Wireless Sensor Networks (WSNs) are an important tool for monitoring strategic and dangerous sites where high security is required. Failure detection for sensor nodes in this specified application is a major concern. The failure of any system may cause losses such as economical, equipment damage and even risks for human lives. Moreover, failures are unavoidable in WSNs due to hardware constraints, hostile environment, unattended deployment and limited resources. This paper proposes a fully distributed approach, called Boundary Node Failure Detection (BNFD), for an efficient boundary control based on the determination of the WSN boundary. This one is determined using an algorithm which has the property to determine in each iteration the one-hop neighbor of the current boundary sensor. Hence, each boundary sensor knows its direct next boundary neighbor and can communicate with it in order to periodically test its presence. When a situation of failure is detected, a network restructuring will be launched to find a new boundary and an alarm will be triggered. The proposed approach has been implemented and simulated with the Castalia simulator. The simulation results show that the proposed method is energy efficient.