Please don't tie yourself (or have anyone else tie you) to a gravestone. Believe it or not, ropes, even "grass ropes", can damage the finish or even the stone itself -- especially the old ones of marble.

Stone isn't as hard as you think!

Besides, you could be tied to one and in the throes of passion pull it over onto you and/or someone else. Nothing like a few hundred pounds of rock landing on you to ruin the mood of whatever you're in the mood for.