Can I make external property persistence on database?

The persistence source code has not been released at this time. However, the next release of AgileTrack is nearing completion (within a couple weeks I expect) and one of the new features is the ability to add custom data fields to issues, projects, iterations, releases, and users.

The way it is set to work is that you can define any number of field names and labels. A combo box is automatically added to the bottom of the record views. The combo box accepts any string as input. It also is prepopulated with previously used values.

That should allow for reasonably flexible custom data to be stored with records. It's not too late for more feedback about this feature. Let me know how it sounds.