I know this is a little old, but like JCrowfoot said... freezing works well. I've used it successfully, but in a small jar at the bottom of the freezer. (That way no one will put it in a drink.) There are also versions that uses vinegar that I've read before, but it was described in a way that would be a no-no if you're Wiccan.
The good thing is that you can adapt it so that it's not necessarily harming anyone else.
Sorry to bump this back up, but I just wanted to second the idea of freezing. I agree with the person who said that people should know what they're doing before they try such things. But the freezer is the only method I have tried, and it has worked well every time. Other ideas I've read about, most of them seem to be a little questionable to me. Whereas the freezer seems to be harmless.
I was really surprised by the responses to this question. Just because someone is gossiping or telling secrets about me doesn't necessarily mean that I told a secret to anyone. Someone might have made an assumption that is correct, or actually witnessed me doing something that is really no one's business. I think there are a lot of other situations in which one could have others telling "secrets" without having told anyone anything. And sometimes there are situations where we need a little assistance.