I think slander is usually understood to mean something spoken out loud, whereas something written would be libel. I'm not really qualified to give legal advice -- just repeating what my lawyer told me some time ago. Slander is probably more difficult to prove, but with libel the injured party would have something written to produce as evidence. Unless you have deep pockets, it does seem less likely that someone would come after you in a civil suit for libel -- but isn't libel actually a crime in some states, with jail time or fines possible?
ARB