Clustering in Wireless Sensor Networks (WSNs) is considered an efficient technique to optimize the energy consumption and increase the Packet Delivery Rate (PDR). Most of the proposed clustering protocols assume that there is a Line of Sight (LOS) between all the sensors. In real situations, there are obstacles which could interfere this LOS. Moreover, most of the available WSNs simulators assume the use of optimistic path loss models that neglect the effect of the obstacles on the PDR. In this paper, we adopt an obstacle-aware path loss model to reflect the effect of the obstacles on the communication between any the sensors. The Castalia simulator is then adapted to use this the proposed path loss model. Moreover, we propose an obstacle-aware clustering protocol, the NSGA-based, Non-LOS Cluster Head selection (NSGA-NLOS-CH) protocol, to solve the CHs selection problem in WSNs with an irregular field. Simulation results have shown that the effect of the obstacles on the PDR cannot be neglected. Moreover, NSGA-NLOS-CH outperforms other competent protocols in terms of the PDR while maintaining an acceptable energy consumption at the same time.