Prevent a hard drive from being formatted?
I think what you are asking is impossible to achieve. If a user has admin access to the drive they will always be able to format it. The only way to achieve this is to not allow anyone else physical access to the drive. If someone plugs your drive into their machine they can do whatever they like.
- Make a backup
- Format the whole drive in one big partition put some random files, a couple of pics and a pdf etc
- Create a large truecrypt file called "Grizly's Encrypted Medical Files"
That way, people won't confuse it for an empty drive, they can see its got something critical on it, assuming they can read, and they are not automatically prompted to format should they shove it in their mommies puter.
Of course, if they can do that, then they can just delete any truecrypt file too.. the only actual way, is LowTek.. lock and key, lasers and dogs.. steel and concrete.. like a buried safe, with monitored alarm system and seismic detectors.. or in a bank vault.. surrounded by storm-troopers.. you get the idea.