How do I insure a business conversation remains confidential?

There exists a set agreements called "Nondisclosure Agreement" and "Nonuse Agreement".  A Google search will turn up a number of hits on example agreements.  Although I cannot endorse any of them and they would need to be modified to your specific needs they will provide you with a good starting point and an attorney can make any necessary final adjustments.  Note that if a business could prove that your idea is ordinary or obvious then it could serve as an argument that there was no agreement formed because they got nothing of value in exchange for their promise not to disclose.  The reason for this is that the law of contracts holds that an enforcable bilateral contract is a contract where promises are exchanged for consideration.  So basically you are promising to give valuable information to the business in exchange for their promise not to disclose or use it.  If you do not give valuable information to the business then the business would be free to disclose it or use it.  My advice is to do some research on the internet on these agreements and then meet with an attorney to draft an agreement that will be enforcable in court.