Auto-unmounting secure partitions

[linux.crypto@charsley.com (Mark Charsley)]

I've got a encrypted partition set up under /secure. I'd like the 
partition to be unmounted after no-ones used it for, say, 30 minutes. I'm 
guessing that there are already tools available to do this, so in order of 
preference, can people advise me
- which fstab/mount option to use
- which command line tool to use
- which command line tool will tell me whether any process has a file open 
under /secure and/or /dev/hdb6 (so I can write a script to run under cron)
- which API call to make in order to tell whether any process has a file 
open under /secure and/or /dev/hdb6 (so I can write an executable to run 
under cron)

Many TIA

Mark
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Linux-crypto:  cryptography in and on the Linux system
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