Ideas are a dime a dozen (I'm sure you've heard that enough times). Ideas cannot be patented so you're left with a choice to execute on your own or share it with guidance.

An immediate action item would be to:
1. Create an NDA (you can find templates of these, just fill in the blanks).
2. Vet the consultant.

Keep in mind, people are working on their own idea and own thing, adding yours to their mix may complicate things and is unlikely to be stolen.

Another point which is super important, execution far exceeds ideas. Knowing what to do with something that you have is a lot more difficult than you think. Listen, don't spend so much time on whether or not an idea will be stolen because you really only have 2 options:

1. Tell someone that can help with a chance for them to steal it or not.
2. Keep it private, which will lead to nothing happening at all.

Hope this helps!