Preventing access to mounted volumes for non-admin users
Basically just take the permissions applied to your own home folder and apply them to the mounted volume. For example try sudo chown -R /Volumes/name-of-secure-volume yourusername:yourgroup

Then use chmod -R 700 to change permissions so that only owner can access them, and group cannot edit or view (in case new users are members of the same group as you). Of course, if new users are able to sudo, then all bets are off unless you put the volume into a TrueCrypt container. Which might be easier.