It's practically impossible to stop anyone copying your posts etc, I'm afraid.
"Copyright falls under the auspices of intellectual property law and protects the rights of creators of original works of authorship whether the work in question is published or not. Original works of authorship include literary, dramatic, musical, and artistic works such as poetry, novels, movies, songs, computer software, and photography. By law, when something is written, drawn, photographed, etc., its copyright is automatically owned by the author. In other words, a copyright exists at the moment the work is created."