Let's say you have 3 BTC worth it UTXOs you can spend.

After the fork, you will have 3 BTC and 3 BTCu (where BTC is core and BTCu is unlimited)

However there is no way to prevent a transaction from being transmitted to miners on both chains. So you what you have to do, is set yourself up so that your UTXOs are not valid on both branches.

Launch a BU client and buy some dust mined in BTCu branch. Create a transaction that sends all your coins PLUS the dust to yourself.

The result in only spendable on BTCu branch because it is not valid on BTC core branch.

Now your value is separated and you can't accidentally create a transaction that is valid on both chains and you still have 3 BTC on both chains.

I suspect within six months, one of the chains will either fail or value will drop to near 0. We'll see.

But if I gamble on Unlimited and do all my transactions on unlimited and then unlimited fails - I will still have 3 BTC on core because I made sure my transactions after fork are not valid on the core fork.