The simple answer is: you can not protect yourself from ideas getting stolen.
The best you can do is to use, as already suggested, NDA's for everyone involved. Even then you will not be able to protect yourself fully as there can be several methods to achieve the result your idea targets (especially in the software world).
My advice is to not pick the "first and best" developer(s). Do research on the potential team you want to hire, look at references, run-time, customer list (if possible). It doesn't have to be a huge company. Have a meeting with them before hiring to get to know them, see if you connect well and so forth. This will help you making a better decision in who to hire.
When it comes to patenting: you cannot patent or copyright ideas. This is a common misconception. You can only copyright a manifestation of an idea (ie. think chair, no one can copyright a chair itself, only the design for a chair). Patents cover methods and they need to be unique and non-common (which is very hard to achieve in software development - and there exists many questionable grants for patents in the software world - but that's another topic).
However, if you do feel you have a unique method I would recommend you patent it anyways. This way you'd at least have a legal card later if someone else uses your patented method without permission. If not, you could end up being the one using the method illegally if someone else comes to the same method and patents it.
