Restrict access to Time Machine Disk?

Question

I'm hoping I'm missing something simple here, perhaps someone can enlighten me:
I've set up an external drive on a new dual band Extreme Base Station to act as the Time Machine volume for all of my family's computers.
In order to get the backups working without user intervention I have to enable file sharing on the disk in Airport Utility, and then because I have "Secure Shared Disks" enabled, I had to make sure the password was saved in each user's keychain (at least 1 per computer).
My problem is that this now allows users access to the sparse images on the time Machine Disk.
Can anybody suggest a way to restrict access while maintaining automatic Time Machine backups in the background? Like I said, I feel like I'm probably missing something as this seems like it should be a standard feature, no?
Thanks!
Jake

Answer 1

Hmm, two points come to mind (again, with the caveat that I don't have any of the equipment and can't test or check anything).
..."I think the reason this doesn't work as we'd expect is that it would kill the ability of TM to back up to the network disk when logged in as anything other than the Admin user."...
I don't think that's right -- if the password is stored in the "System" keychain, it shouldn't matter whether or not anyone is logged in. Just to make sure we aren't talking about different things, I was referring to the "System" keychain, not any individual users' keychain, including "admin" users or the "root" user. A user's login keychain would not normally be unlocked (requiring the user's password) unless they log in, but the system should have access to the "System" keychain whenever it needs it.
..."Even if I could hide just that particular share in the Finder sidebar, I'd be happy with that."...
That raises an important point that I had previously overlooked -- initially, when I had raised the possibility of restricting file access to the backup itself, I suggested that restricting access to the password would be better. However, upon further consideration, it would probably be preferable to do both, because while restricting access to the password would limit users' ability to mount the share and look at backups whenever they felt like it, it might not prevent them from browsing backups while the system has mounted the remote volume and is in the process of performing the backup. That too would depend on how things are mounted (which I have no way of checking).
Just something to keep in mind while you are experimenting...