[user104658]

Originally Posted by The Slim Reaper

I'd come to an agreement beforehand with the person, that would then be put into a legal contract

I mean, that is the basis of a prenup isn't it? Or it's supposed to be, anyway, it can have whatever both parties want in it. Obviously sometimes people will abuse that/set all the terms themselves/make ultimatums or simply say "it's sign this or no marriage" but TECHNICALLY it's intended to be a mutually-agreed contract.

From what I've read most of them don't really stand up to a good going over in court anyway; there are usually elements at play that weren't considered in the original contract and so plenty of "loopholes" for a good lawyer to exploit.

Of course the famous one in Alf's Liar Liar example, that she was actually younger than she said, and while she was old enough to get married at the time of the marriage and prenup, she wasn't old enough to sign a contract without a co-signature from a parent or guardian, making the marriage valid but the prenup invalid. Movie gold, obviously.