Protection barriers against the fall of boulders and rocks are structures with non-linear mechanical behaviour that make the study particularly complex. In this study, the understanding of an experimentally observed variability was investigated numerically using a non-linear spring-mass equivalence. First, key figures of the experiments on which this study is based are detailed. Then, the numerical model for the dynamic simulation of the barrier deformation under impact is presented. Finally, the variability due to block-related parameters and then net-related parameters are explored and evidence the role of the cables’ geometric stiffness in the global response of the fence.