Okay. So you trust them to use your computer and you also think they know nothing of how to get around security through obscurity, but you don't want them snooping around your NTFS drive?
If that's the case, you might be able to make access to the NTFS drive inconvenient, but it'll be inconvenient for you as well.
Paste these commands in the terminal: Check to see what your NTFS drive is called. Let's say, for this example, it's /dev/sda1
Comment out (put a # sign in front of) the line that already refers to /dev/sda1 (or whatever it's UUID is). Then add a new line
sudo umount /dev/sda1
sudo mkdir /ntfsdrive
sudo nano -B /etc/fstab
Then save (Control-X, Y, Enter)
/dev/sda1 /ntfsdrive ntfs nouser,noauto,nls=utf8,umask=0222 0 0
Now, if they double-click the drive, they'll get an error message saying they can't mount the drive because they don't have permission. To mount the drive, you will need to issue the command
sudo mount /dev/sda1