Knowledge leakage poses a critical risk to the competitive advantage of knowledge-intensive organisations. Although knowledge leakage is a human-centric security issue, little is known about leakage resulting from individual behaviour and the protective strategies and controls that could be effective in mitigating leakage risk. Therefore, this research explores the perspectives of security practitioners on the key factors that influence knowledge leakage risk in the context of knowledge-intensive organisations. We conduct two focus groups to explore these perspectives. The research highlights three types of behavioural controls that mitigate the risk of knowledge leakage: human resource management practices, knowledge security training and awareness practices, and compartmentalisation practices.