You’re so right about not letting the fear of your idea being stolen get in the way of play testing your concept! I had such a huge fear of my game name being stolen at first that I didn’t tell anyone the name, and event went so far as to create an NDA. That was totally unnecessary. But if you’re paranoid like I was, you could always write your idea down (name and all) in a letter, send it to yourself, keeping that letter sealed. That way if you ever need to prove you had the concept first, you have your evidence.