Localization plays an important role in wireless sensor networks, since sensors need to associate their readings with location in order to deliver meaningful information. A promising approach to enhance the robustness and the security of localization is location verification, where the objective is to verify a node's claimed location. In this paper, we propose a new location verification protocol, where verifier nodes vary their communication range in order to triangulate the position of a node. We first present the network model and our assumptions, followed by a detailed description of the protocol. Next, a security analysis is provided which shows that the new approach is robust against several location spoofing attacks. Moreover, we derive both analytical and simulation results for the coverage probability and show that a high coverage probability can be achieved with the new protocol, even with a relatively low density of verifier nodes. Finally, we study the impact of localization error on the verification probability and demonstrate that the protocol is sensitive enough to detect small deviations between claimed and actual locations.