[abh19]

In lieu of software password and encryption, I think you should be able to put your database file on an encrypted disk image. If you haven't done this, the process is: go to Disk Utility, create a new image, choose encryption and a password. Then drag your omnifocus database file into it. When you want to open omnifocus, double-click on this database file instead of the application icon.

OmniFocus wants your data to be in the Library/Application Support/OmniFocus folder, so this method isn't officially supported. You may run into problems, so make sure to keep it well backed up. Also, make sure that your backups are being saved to the encrypted volume rather than to your documents folder.

By the way, what problems are you encountering with filevault?