Casinos easily track their patrons and how much they are up/down
They do? And isn't there a hostload of illegal joints, bookies and dealers where there are no receipts and/or control?
How about: I took all the money out in cash, because I'd rather gamble it away than let that bitch get it, then I went to Las Vegas, and I lost some 10K at Casino Royale (provable), then I went for a drink in a bar, where I met a gentleman who invited me to a private high stakes texas holdem party, and I got really drunk and lost the whole lot.
How could it be proved that the cash still exists? Would the judge rule that the man has to pay half of what he had prior to the trip? What would the difference be in reality whether a business slowly drained money away or if you lost it all in a moment of foolishness? The end reality would be that it was all lost permanently.
Perhaps the phrase 'I'd rather gamble it away than give it to the ex-wife' wouldn't go well with the court, but I can think of a number of other scenarios where a man could "reduce" his net worth without the money being lost forever.
I would think such cases could be really hard to investigate. Don't you need very hard proof the money still exists?
You can make up any story/scenario but in order for it to be accepted the Judge would need to accept it.
A business slowly draining the money away is much more audit-able then one foolish mistake. It is also something that would be caused by a bad economy/market (something out of his control) as opposed to one foolish mistake is caused by poor judgment.
Unless he had made one very good investment it is likely that he has a substantial amount of income that would generate and grow his wealth to get it to be where it was before it was "gambled away" so he could simply have more of his earning taken (or possibly garnished) if his assets were to "be lost in a bad bet"