Nope. Not hard at all. Start a joint savings account or a CD with a trusted family member or friend and have them hold the documents.

Buy gold krugerrands. Bury them in a tin in your own yard or other safe location.

Prepaid Visa/Mastercard like Green dot. Load it and keep it at work, with a confidant, hidden at home, etc.

Buy a valuable antique/collectible that can be resold easily. One that your abusive partner is unlikely to realize the value of.

There are plenty of ways to hide money for an exit strategy available to anyone.

The real issue is recognizing it as a viable preemptive strategy against abuse, making it part of the marriage process BEFORE you get married, or being able to come up with the money in a secure and discreet way after you are married if you didn’t prepare beforehand.