Here’s the thing, as a startup incubator Director, I deal with this question all the time. Seriously, WAY too frequently.
If your idea can be stolen and you can’t compete with that, DON’T START!
Advice that the right contracts and agreements can protect you are crap, driven by people who still perceive such things work OR lawyers who advise and sell that. Anyone can take any agreement and work around it. Any big company can outspend you in court over IP, patents, etc.
STOP thinking that ANYTHING can prevent someone else from competing with you. You will never succeed if you think that way.
The only thing that matters is that you can out execute the success of the business: The marketing, the partners, the cash flow. Getting something built is NOT a business.
Have them build it. If they can take it, build it differently than you, and make it successful despite you, frankly, they deserve to as you shouldn’t be making it a business if you can’t. Sorry for the harsh reality check but that’s the bottom line. Start this because you CAN; and/or find and start with the team of people who are as committed as you to doing it AND doing it together.