Satanist messages in songs?? .... Why not use backmasking techniques (using a reel-to-reel tape recorder and playing the song backwards)? ...
As illustrations:
Led Zeppellin's Stairway to Heaven
The Beatles' Revolution Number Nine
I'm not a follower of it ---since it can easily be manipulated into whatever the person making the backmasking tape -- into anything he feels like saying in his message.