In wireless sensor and IoT networks dedicated to smart-cities, a leader node performs critical tasks such as generating encryption/decryption keys. In this paper, the leader is the node situated at the extreme left of the network. It is the node which starts the algorithm of searching the boundary nodes. These nodes will be used to monitor any sensitive, dangerous or inaccessible site. For this type of application, the used algorithm must be robust and fault-tolerant because it is difficult or even impossible to intervene in the presence of node failures. If this node is the leader, such a situation can be catastrophic. In this article, we present a new algorithm called DoTRo, which is based on a tree routing protocol. It starts with local leaders which will launch the flooding process to determine a spanning tree. During this process, their values will be forwarded. If two spanning trees meet, the tree that routes the best value continues its process while the other tree stops. The remaining tree root will be the leader. This algorithm is low energy consuming with reduction rates that can exceed 85% with respect to the classical minium finding algorithm. It is efficient and fault-tolerant since it works even in the presence of node failures and communication disconnectivity. Additionally, the energy consumption is well balanced between nodes. Finally, the complexity and the proof of convergence of the proposed algorithm is presented.