Mobile Ad Hoc Networks (MANETs) are becoming more pervasive thanks to their advantages of being infrastructure less and portable. However such networks suffer from a variety of attacks due to several inherent factors such as mobility, signal attenuation and interference, and limited computation power and battery resources on mobile devices. Secure light-weight routing for a reliable path consisting of trustable nodes has not been an easy task. In this research, we propose the Secure Last Acknowledged Packet Routing Algorithm (SLAPRA), capable of efficient and prompt attack detection and malicious node isolation, and demonstrate the validity of the algorithm through simulation.