Security in the Internet of Things (IoT) remains a predominant area of concern. This survey updates the state of the art covered in previous surveys and focuses on defending against threats rather than on the threats alone. This area is less extensively covered by other surveys and warrants particular attention. A life-cycle approach is adopted, articulated to form a "defence in depth" strategy against malicious actors compromising an IoT network laterally within it and from it. This study highlights the challenges of each mitigation step, emphasises novel perspectives, and reconnects the discussed mitigation steps to the ground principles they seek to implement.