Mobile Ad-Hoc Networks (MANETs) are particularly useful and well-suited for critical scenarios, including military, law enforcement as well as emergency rescue and disaster recovery. When operating in hostile or suspicious settings, MANETs require communication security and privacy, especially, in underlying routing protocols. Unlike most networks, where communication is based on long-term identities (addresses), we argue that the location-centric communication paradigm is better-suited for privacy in suspicious MANETs. To this end, we construct an on-demand location-based anonymous MANET routing protocol (PRISM) that achieves privacy and security against both outsider and insider adversaries. We analyze the security, privacy and performance of PRISM and compare it to alternative techniques. Results show that PRISM is more efficient and offers better privacy than prior work.