- Find a Software development plan template somewhere - google it
- Get a trusted developer from
https://www.upwork.com - make sure you read all the reviews and check the refferences.
- Dont give away any details in the description of the project
- Make them sign a NDA before you hand over the Software development plan. It wont prevent them from stealing the idea, but you can sue afterwards if they make millions.
I have done that many times now, and never had any problems. If the conde they make dont live up to whats agreed upon, they just keep the money until they have delivered, or find a new freelancer. The platform is brilliant