Make your main developer, who has access to all information, a partner. Pay your other employees decent salary with bonuses for good work. I don't think there is any way to completely protect yourself from anything like this in startup, you need just trust people and do your job fast, so nobody would be able your code before you or in the better way you did.

Cover your ass - make sure you have a clause in your employment contract that states that committing acts such as x,y,z is prohibited and warn them of what will happen if they do so.

In your employment contract, you should also note that the copyright holder of all the code produced by your employee whilst working on your projects belongs to you and you alone.

In addition to an employment contract - you should have a NDA None Disclosure Agreement.

The aim of clauses and NDAs is not to try and scare people, it's all about making sure that they know what is allowed, what is not allowed and what will happen if they do these things that aren't allowed.

Do yourself a favour and talk to a business solicitor who could create the employment contracts for you - seeing as we web developers aren't great with "Legalese" we may miss some things here and there.

HTH. :)

1. use source code tools
2. hire peoples who there religion forced them not to take any thing from your company behind your back, and be sure that they follow the rules of there religion!!!
3. dot' let one person have the code for the complete solution, use OOP methodology in programming solution.