One strong thing to consider when implementing any "code theft prevention" scheme is the fact that you're willingly trading productivity for security. The most productive environment for creating and debugging code is an open and easily shared one. This is why there are millions of lines of Open Source code written every year, even though most people involved aren't being paid for it.
Consider carefully whether the increased overhead and costs in terms of developer time is worth the theoretical potential for theft by one of your developers, who is already familiar with your algorithms and architecture, and could probably re-create the code if it was really something worth stealing.
Now, protecting your source code repositories from external access, and protecting your code "in transit" from people external to your development group who might be stealing it really boils down to Network Security, and you'd probably be better off posting it on serverfault.com or superuser.com