How do you prevent hired developers from stealing code?

I'm in the process of opening up a company that will eventually hire 2-5 developers to work on a large web app.

My main concern is that one or more developers could steal the code. I could make them sign contracts against this type of thing, but I live in a country where the law is "bendable".

Is my only option to lock them up in a room without inet access and usb ports?

I'd love to know how others have solved this problem.