Unix system version clobbering

[dmitchell@BACKUS.trc.amoco.com (Donald H. Mitchell)]

Architectural background

I'm storing my files under a .sct directory on a Unix fileserver using NFS as
the access mechanism.  The user property nfs-generation-retention-count
controls how many versions of each file the symbolics will keep under a unix
directory.  The default value is 5.

Problem

Ok, now I want to use defsystem to create and manage multiple versions of
systems.  I like the idea of using the retention count control mechanism; so,
first I tried setting the files' protections (file attribute) to 444 (read
only).  I then merrily began editing the files further; however, when I did a
dired, my protected files were gone!  The retention control mechanism ate them
even though they were protected!  Protection mechanisms don't save you from
the grim reaper (notice that this problem is under the Symbolics's control).

"Ok, just handle generation retention by hand and set
nfs-generation-retention-count to some absurdly large value", you say.
However, all I need is one new user to get on the system and edit a file and
all the preciously saved versions are gone (don't forget that
nfs-generation-retention-count is a user property)!

What do I do?  Go back to changing file names after each version is complete?
Use a lmfs partition (yuch!)?  Set some global retention count control
variable that I can't find?  Advise the save file routine not to delete
protected files?