There's not a lot one can do. It's sort of like preventing your bodyguards from assassinating you. They know all your procedures, it's a matter of trust. Even as a tech co-founder, it's difficult to control as it's easier to hide back doors and time bombs as the code gets more complex.

There's a few measures you can take: 1. Daily backups of code repositories, on a computer you trust. 2. Periodic backups of the production server. 3. Check your contract agreements on IP with a proper lawyer. IP is very sensitive as a lot of techies also have side project.

But in general, trust your techies. People are reciprocal. If you start putting in more safeguards, they start putting in their own. Don't isolate them from meetings/clients, don't put too many levels of security, don't hire people to "check up" on that guy, trust the intern.

Most engineers just want to build stuff. If you let them build stuff they will be very happy and loyal.