Josh Berkus' "Safe Data is Happy Data" (originally entitled "Lock Up Your Data") goes talks about defense in depth -- going beyond firewalls and other "perimeter defense" mechanisms such as middleware and web server tools. Berkus explains "full-stack security" including preventing SQL injection, data abstraction, database permissions, and even what to do after an attack.
Stream directly online at http://technocation.org/node/591/play or download the 346 Mb .wmv file at .
From the official OSCon description: