The ability to protect an idea is similar to protecting a trade secret, You need a non-disclosure agreement. But the best protection is to know your audience before disclosing your idea. Since an NDA is a contract, you must know what you must have in it to protect your idea. And you must write that contract as if there was already a breach. Overall, an NDA coupled with your best judgment on who you disclose your idea to is the right place to start.