Should a man assume this is a real possibility before he marries the young lady, why marry her at all? Same goes for the young lady. If she believes the man may leave her or beat her or cheat on her, etc, why take the risk?
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The solution is not to take precautions on paper but to do the best you can to make a good choice before marriage, pray for each other a lot, and leave the rest to God.
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He will take care of you if you do the best you can and trust in Him.
Legal precautions can be circuмvented if the woman has lost all regard for the moral aspects of the act. She can claim abuse for instance. Ah, yes, the wicked husband severely spanked one of the children (this can be exaggerated). Despite what Pax says, it doesn't have to be proven in a criminal court in order for the divorce judge to factor it in. Women could have affairs without ever getting caught, etc. As you say, the only true precaution is finding the right person. And you don't go on how she presents herself while dating. You look at her family, her upbringing, and signs of her being devout. Look for women who, without being forced to by their parents, dress modestly and are devout beyond the mere requirements. Look for women who attend weekday Mass or have a strong prayer life. Then your odds of a stable marriage increase dramatically ... if you yourself have the same qualities.
And then, if despite all this, God wills to bring you the cross of an unfaithful wife, well then it's His will that we suffer those things for our sanctification. We have the opportunity to turn the other cheek and become holy in our forgiveness of such a great offense.