Volume (disk/pack) labels are, in general, the `right way' to do
this:  the label on the disk says what is on the disk, and no matter
where the disk is found (even on another machine!) the data and
label have moved together, so the label is still correct.

As a first cut, the obvious thing to do is to have a program that
checks /etc/fstab against the disk and/or FFS `last mounted on'
fields.  If they agree, all is well.  If they disagree, the program
can either get help from the sysadmin or (for those who like to
live dangerously :-) ) rewrite /etc/fstab.

Note that such a program must be moderately clever in case a drive
holding /usr moves from `box A' to `box B' where box B already has
its own /usr.  (In the case of FFS, there are also endian-ness
considerations, for drives moved from one machine to another.  The
`last mounted on' field is a byte string and hence non-endian, so
some other guard is required.)

Chris