Help request from a non-developer

Hello all, new to this list, hope I'm not asking a question that's
been covered already.

A little background :
I'm a project manager / technical sales guy. I've got a
quasi-volunteer developer working on an elderly (meaning it's been
around and actively, if sloppily, developed for some time) Zope 2 app
for me. Since time immemorial it has been coded live on the production
server. Originally this wasn't a problem as it was a one man show, if
he broke it, it was his fault and he suffered. Since then the project
has grown and I want to put in place a development server.

The issue :
When I really pushed for him to develop off-line, he did so on a local
copy of the site including a snapshot of the ZoDB. When he pushed it
live he pushed up the (now out-of-date) ZoDB and squashed the new
data. Obviously, not cool.

So, the question :
How can I set things up (or rather ask someone qualified to set things
up) so that there is a development server to code and test on (with
real data) and a production server that's relatively easy to push up
the code to once it's signed off on without squashing the live data ?

Thanks so much for your help,

Christopher Appell