As we've learned watching the Rethuglicans lately, the assault on abortion rights is only the first step — they also want to shut down the wickedness that is contraception. But they're not going to stop there, oh no! If you want a peek at our theocratic future, read this incredibly long-winded disquisition on exactly what you are allowed to do even in the marriage bed. Everything is forbidden, except vaginal penetration and the ol' in-out. You aren't allowed to even do these things as foreplay, culminating in procreative intercourse.
The expression 'that use which is against nature' refers to unnatural sexual acts, such as oral sex, anal sex, or manual sex. Saint Augustine condemns such acts unequivocally. He even states that such unnatural sexual acts are even more damnable (i.e. even more serious mortal sins) when these take place within marriage. For God is even more offended by a sexual mortal sin that takes place within the Sacrament of Marriage, since this offense is not only against nature, but also against a Holy Sacrament.
Dang. Well, at least Augustine didn't explicitly forbid rubber wetsuits, fuzzy handcuffs, vibrating crucifixes, octopus, ceiling-mounted swings, clamps, chocolate pudding, flavored lubricants, Wonder Woman costumes, rubber chickens, exotic headware, whipped cream, video cameras, Silly String, roller skates, trampolines, nitrous oxide, balloon animals, feather boas, ball gags, or bungee cords, or I might be going to hell.
It's amazing how much detail Catholics will go into documenting why people shouldn't do the things that they all do anyway. You might even call it loving detail.