@Blaise Doremus about the best you can do is an NDA (which actually hold very little weight if broken). There are 2 things you can do.
1) Start going to developer meetups and network with people. Find someone who you can have a mutually beneficial relationship with and nurture that until you trust them enough to work together on your app. The advantage of this is that you are less likely to have your idea stolen. The disadvantage is that you’ll probably have to share equity in whatever you create unless you afford to pay a US software developer wage (approx. $85k annually)
2) Hire individuals off freelance sites to develop parts of the app and learn to integrate the pieces yourself. This helps reduce the chance of a freelancer stealing your entire code and becoming your competitor, but you’ll still have to learn enough to put the pieces together.
In the software world it’s almost impossible to protect your product. If people work on it, it’s likely someone will “borrow” pieces of it. People even steal Microsoft product.