Consent is a very big deal in my marriage. There is a specially designed pad on my wife's night stand, and nothing happens until that consent is signed, and dated by both of us. We've opted to not require witnesses so things can be a little less formal and we can have a bit of spontaneity. She then holds the form in her hand while we're making love so she can crumple it to revoke consent any time she wishes. I make a point of not letting her reach orgasm very often lest she crumple the consent form in ecstasy and confusion arises. We both insist it's better this way.

...none of that is true, except the parts about consent being a big deal, and witnesses. Unless you count pets. They can watch, but not from on the bed.