Even just a very thin encryption layer would probably do a decent job. Attackers are typically going at it from an infrastructure perspective: they make a hole, poke around for basic configuration info, locate the database, and siphon it out. They may or may not have enough time and knowledge to reverse-engineer a basic column-specific symmetric scheme.

The only drawback is that such scheme must then be made available to any system that consumes the database, possibly from multiple languages.