Hire a lawyer to write a work contract and NDA (non-disclosure agreement).
Require the programmer to sign the NDA before you discuss the project. You can give a general sense (a web based system to do e-Commerce). A professional will sign without any complaint. Look for a different person if they give you any grief at all regarding the NDA. The NDA is your primary means of protecting yourself if they share your idea with anyone else.
This is a really bad idea. Reputable professionals won't sign your NDA. I already had a kid on this forum ask me to sign an NDA - what a joke. Only someone who doesn't take you seriously will sign it, and it won't be binding because you'll be unable to enforce it.
No-one is going to try to steal your idea unless it is already wildly successful. Even if it is a great idea. Recognizing a great idea is a rare skill. Recognizing a great execution is trivial. Worry about the second one.