Well it's one thing to MAKE someone lie down on a towel during sex, and another thing if it's just to avoid a mess (esp. blood, which stains). When I'm on my period, ktstpktsp and I put down a plastic grocery bag and then a few paper towels on top, which works great (a little crinkly, and I have to stay on the bag for the serious thrusting, but otherwise fine) and has never made a mess. That's about the only "cleanliness" precaution we take though... I mean, showers are great, but they're only really necessary before rimming (see other thread in Sexuality!) or if things are starting to get ripe...
