Are people expected to have consensual contracts, perhaps even live-in lawyers and witnesses to protect them from their own spouse too? 

My wife and I made a deal with each other, that neither one of us will EVER deny the other sex, even if we're not really in the mood. (Excluding any painful, weird or kinky stuff.) It's not penned on paper though, so I suppose she can renege any time she wants. Call ME old fashioned, but I consider a marriage certificate (or its equivalent) an eternal consent form. (At least until death or divorce do you part.)