Defense-in-depth is based on the principle that, while no security is perfect, the presence of many independent layers of defense will geometrically increase an attacker's difficulty in breaking through the walls and slowing them down to the point where the effort to carry out an attack is not worthwhile. Each layer multiplies the effects of the previous layer. If the outer wall deters 90% of attacks, and the inner walls deter 90% of attacks, then in combination they deter 99% of attacks. Defense-in-depth defense techniques place core assets behind varied and individually effective layers of security, each of which must be circumvented for an attack to succeed. There are many options provided by your compiler that can help you mitigate known attacks such as buffer overflow without touching a single line of code. In this presentation, we will take a historical look at the mitigations proposed over time by cybersecurity researchers, and how they have been violated, forcing the development of new and ingenious countermeasures.