Not sure which networking platform you're using, but if you revoke permission to delete files at the folder (rather than file) level, this has two effects:
1) The master database can't be deleted but can still be written to.
2) The first user will create an LDB file, but it won't get deleted when the last user closes the system.
It doesn't matter though, because later use of the DB will re use it.
To revoke delete permission:
On Windows 2000/XP/2003:
On XP you need to turn off simple file sharing first.
Right click the folder, choose Properties. Click on the Security tab and highlight the user or group of users you want to set permissions for. Untick "Inherit from Parent the permissions" and choose Copy. This will define permissions for that folder as explicit rather than inherited. (Ensure that you give yourself or a group you are a member of full control on the folder).
Click OK.
Right click the folder again, properties. Click the security tab and highlight the user or group you want to set permissions for.
Click Advanced, highlight "Full Control" from the above folder, click Edit... then untick the Allow column against Delete Subfolders and Files.
Click OK on the Permission entry for <x> screen. Click OK on the Advanced Security Settings folder. Click OK on the folder properties screen.
If this folder is shared for network access, you can get away with change level permission on this folder (full control not required).
If you are using a Novell Netware network, things are a little different: use the inherited rights mask to remove the Erase permission from the folder.
For anyone using a different network system, sorry, not really au fait with it.
John