Hey, this is a great tip. Despite my lack of Terminal experience, it works on my Mac Pro on 10.4.8. However, for other Terminal newbies I want to pass on what I learned...

I echo the comment about the fact that the fstab file does not exist and is created when you sudo pico and save the file with the line in it. There is also a file in etc called fstab.hd, but that isn't the file you're looking for. Don't edit that one.

No other lines in the fstab files are needed. Just the ones starting with the UUIDs of the drive you want to prevent automount on.

At first I did not see the UUID in Disk Utility, and figured out that you have to get info on the volume, not on the disk mechanism. You can then copy the UUID from Disk Utility and paste it into Terminal. Don't forget to add "UUID=" before it.

Thanks for the tip, I really needed it for a machine where I wanted to keep a certain volume offline when booted into the test OS.