Wireless Mesh networks are a new way of deployment of wireless networks. They are based on radio nodes that directly communicate and are organized as a mesh topology. The new challenges of this type of deployment could be classified as: first, the improvement of the Quality of Service (QoS) to use the bandwidth more efficiently and to use different types of services; second, the security to avoid any intrusions or denial of service attacks. We shall focus on the la last point by proposing a new method in this study to secure Hybrid-Wireless-Mesh Protocol (HWMP) for Wireless-Mesh-Networks (WMNs) based on Watchdog. The purpose of using Watchdog is to prevent an attack on the internal nodes and to exclude them from network operations. We have implemented the Watchdog technique in order to secure data exchange in mutable fields. Through extensive ns-3 simulations, the Watchdog-HWMP is able to detect both malicious attacks and selfish behaviors without significant overhead.