While the ability to express routing policies in wireless sensor networks (WSNs) has been well-studied, unfortunately, the ability to enforce these policies has not been. The core challenge is that if we assume an adversarial, decentralised, and high-speed environment, then how can the receiving node be sure that the path being announced by the incoming packet is the actual path followed by it? In this paper we describe the networking primitive, called routing path verification (RPV), which serves as a tool to enforce routing policies and presents a solution to the defined core challenge. We assess the security of the proposed RPV construction in a formal way. More significantly we augment a suitable key exchange protocol with our proposed RPV construction, to achieve an overall RPV scheme. We also evaluate the computational, communication and storage overhead of our proposed scheme and the experimental results show that the approach is quite scalable.