The Defence Evaluation & Research Agency (DERA) has a long association with the field of space debris research. Effort has focused on the development of software tools (IDES and SDS) to model the debris environment and its long and short term evolution. These models are now well established and recognised for their distinct capabilities. More recently, DERA has begun developing a new software tool called SHIELD. This is an innovative concurrent engineering model designed to assist engineers in identifying the most cost-effective debris protection strategy for a satellite. The model uses a novel survivability metric technique in conjunction with a genetic algorithm to search for the optimum choice and location of bumper shields, and the optimum arrangement of critical satellite components. This paper briefly summarises the unique aspects of the environment models and recent results, before describing the new SHIELD model in some detail.