I suppose a prenup is a good idea in principle, but in practice it might not work if it signals a lack of trust.
A better idea might be to keep some accounts and property of your own, with only your name on them, in addition to any joint accounts and property. If the worst happens, you can say "I had these before we met". Be fair, though. If you're both paying for the house, both your names should be on it. Some loss of money and things is part of the risk one must accept going into a relationship. Just make sure you've kept enough out for yourself to be comfortable, and be accepting if the partner wants to do the same. Anything you've kept out for yourself should be honestly disclosed, with the idea that anything of sole ownership is still potentially available for use by both, and that sole ownership of some of the money and stuff shouldn't make any difference if the partner isn't just using you and planning to leave you.
This is just good business practice. Marriage is, among other things, partly a business/financial partnership. I know people who have been screwed over in private joint business, too, because they didn't keep enough out for themselves to be comfortable if things go bad.
This money/relationship issue can be a barrier to entering relationships, but it also has significant implications for established relationships. It keeps coming up not because the men here are inept, deluded, or feeling sorry for themselves, but because it is a significant and legitimate concern.
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A boy and his dog can go walking
A boy and his dog sometimes talk to each other
A boy and a dog can be happy sitting down in the woods on a log
But a dog knows his boy can go wrong