As systems become more complex, the potential for security vulnerabilities being introduced increases. If we are to provide assurances about systems we design then we need the means of analysing, managing, and generally making sense of the data that contributes to the design. Unfortunately, despite ongoing research into tools for supporting secure software development, there are few examples of how tools can be used to help build and support design models associated with security and usability. This paper summarises some of our experiences developing and applying CAIRIS: a requirements management tool for usable and secure system design. We describe our motivation for building CAIRIS, summarise how it was built and evaluated, and present our experiences applying it to real world case studies.