This paper focuses on the resiliency of wireless sensor network routing protocols against selective forwarding attacks by compromised nodes. Informally, resiliency should be understood as the capacity of the routing protocol to endure and mitigate the presence of a certain number of compromised nodes seeking to disturb the routing process. To provide for security when nodes may be compromised, cryptographic solutions must be completed by algorithmic solutions considering "beyond cryptography" approaches. In this article, after discussing the shortcomings of existing routing protocols against packet-dropping malicious nodes we describe some protocol behaviors enhancing routing resiliency under several combined routing attacks. These behaviors are mainly based on traffic redundancy and probabilistic selection for the next hop candidates, which permit to exploit and benefit from the inherent structural redundancy of densely deployed sensor networks. We consider the case that compromised nodes, prior to selective forwarding, and seeking to increase its impact, may perform several well known routing attacks such as Sinkhole, Sybil and Wormhole. Several variants of the well known gradient-based routing protocol were tested and simulation results show that using the proposed techniques resiliency can be improved. Nevertheless, as expected, resiliency comes at a cost and our results also shed some light on the resiliency-energy consumption trade-off. We propose in this paper the behaviors enhancing the resiliency of routing protocols under several combined routing attacks.