As I am sure you are all aware, database hacking is happening--afterall it's where the crown jewel--you data--are located.  I came across this article today and it was very helpful in terms of how a hacker could get through a system with as little footprint as possible and how to think about protecting your systems. 

Cesar Cerrudo is a Security Consultant and Lead Research for Application Security Inc and he presented recently at Black Hat 2009.  His paper was on SQL Server Anti-Forensics: Techniques and Countermeasures.  The paper talks about anti-forensics (which is about how a hacker covers/removes traces of their activity) and the counter measures you can take to help reduce or mitigate the chances of them reducing their tracks when they have invaded your system. 

This is a must read and make sure to check out his other articles!