Existing approaches for clustering wireless sensor networks by using relay nodes (RNs) suffer from two major problems: impracticability for realistic scenarios and lack of fault tolerance. The first problem is due to the assumption of a two-dimensional Region of Interest (RoI). The second problem stems from the fact that these approaches do not address the construction of disjoint routing paths, where multiple routing paths have common intermediate RNs, which create a bottleneck for the data transport and points of failure. In this paper, we tackle these two problems by proposing a new RNs deployment approach based on more realistic assumptions. Indeed, a more realistic communication model is considered, which takes into account the impact of the RoI topography on wireless communications. Additionally, a practical position constraint is adopted, where the RNs are placed only on the RoI crest points, to minimize the topography impact on the wireless communications. By relying on an efficient algorithm that constructs from a connected graph many Steiner trees, covering the same subset of vertices, the proposed RNs deployment approach selects the appropriate positions of the RNs and ensures a reliable data transport from the sensor nodes to the collector node, according to a two-tier topology while satisfying other secondary objectives related to the cost and the quality of the communication links. The simulation results demonstrate the feasibility of the proposed approach and its ability to minimize cost and improve communication links quality.