...or know that one of the developers had already downloaded a copy of the buggy code (during that 4 hour or so window) which promptly stomped on the bug fix when it got committed.

I'm a little confused by this. Why did the other developer download the script from the live site rather than from CVS (I assume you're using CVS - either that or, when committed, the script is now in some insane asylum somewhere :). If they had retrieved it from CVS, they/you would have seen the conflict at commit time.

What we've found that works is a BSD jail for each developer, and commit direct from the jail or from their machine. That way, we don't touch live code until we have to. Usually, we also need a "hack script" to set up the jail so that it mimics the live environment, but thats often no more than a few soft links to modules etc.

Our versioning system used to be:

1. turn around
2. ask out loud, "Is anyone working on XXX today?"
3. if no, proceed to do work on test server
4. if yes, find out what files they were working on and avoid them like the plague

This actually worked quite well until we went from one room to three rooms :) - but is a method I do NOT endorse anymore - even if you're the only person working on a project.

Perhaps you can gain brownie points for suggesting amendments to your current practice? Or just give that other developer a slap on the wrist and shout "USE CVS" at them a few times?

.02

cLive ;-)