You might be able to compartmentalize the knowledge. I.e., design the source code to be multiple independent modules that communicate through published API's.

You might be able to compartmentalize the knowledge. I.e., design the source code to be multiple independent modules that communicate through published API's. Then each person who has to work the source only needs access to one module. Someone would still be able to steal the module they're working on, and the specs for the other modules it communicates with, but a single spy presumably wouldn't be able to steal all of the modules. I doubt this is much outside of defense/intelligence, though (or even in those sectors for that matter -- look at how much Manning and Snowden had access to). It'd make things much more expensive and bureaucratic, for one, and it limits your top talent by forcing them to stick to their one little slice instead of improving the pie as a whole.