If you write it, copyright it. Probably won't do you any good if Michael Jackson wants to rip it off, bu couldn't hurt. A copyright is only a basis for a claim if a lawsuit ensues.

If you don't want anyone to sing it, don't let anyone hear it. You'll never get royalties, but nobody will rip you off. If you do hope to make money from your efforts, post the song to the DT with copyright notice; maybe someone will find it here and want to record or perform it.

Intellectual property is like fertilizer; it does nobody any good unless it's spread around.

End of lecture.