Two different options:1) Patent it--that provides the best protection, but of course can be costly (it can cost a few thousand dollars) and take several months at a minimum.2) Before showing/disclosing the product idea to anyone, have them execute a non-disclosure/confidentiality agreement which will--a) acknowledge your ownership of the ideab) state that they are being shown the idea only to evaluate a possible business relationshipc) state that they may not use the product idea for their own benefit or the benefit of any other parties; or to disclose it to anyone w/out your prior written consentd) state that upon the conclusion of negotiations, if no deal is struck, they will return everything you provided to them and certify that they have destroyed all copies and notes.