In the age of electronic everything, I have to imagine it can be difficult to explain large cash withdrawals to your wife. What are some of the ways you go about your business without it being noticed?

and make taking large sums of cash out of the bank a regular feature claiming I used it for lunch, parking, office betting pools, etc.  That way she is none the wiser when I use a goodly portion for the hobby

Joint accounts are for bills, maybe I am in the minority here, but my account and how much is in it is none of my SO's business and vice versa. There is a joint account and bill are paid through that account. With that being said, If the wifey needs or wants something then she can have my card to do whatever she needs to do and spend whatever amount she wants, every thing doesn't need to be shared/joint. Last I checked, banks don't limit you to how many accounts you can have.

A wise provider once told me after I asked her advice on exactly that question - you'll figure it out, they all do.

You are a minority here lol. I haven't heard of too many cases similar to yours, seems you got it under control!

My wife is the traditional house wife. I had bank and brokerage accounts and Real Estate before we got married. I always used a PO Box for statements. I've always kept my premarital assets to myself.

Damn. Not a secret anymore.

The wife has no interest in our finances.. as long as the power is on, and the car has not be repossessed.. she's fine.. live & let live.. I just move money into the checking account from other accounts to keep it solvent..

Much easier that way.

I've sold my s/o on the idea that I have a gambling problem.

I have a few legit hobbies that allow me to buy, sell, and trade frequently -- and they typically involve a reasonable chance for profit outside of our joint accounts.  I also normally keep a stash of cash in a large gun safe which is also off-limits to family for obvious reasons. (Spouse has access to an in-room gun safe apart from the larger safe.)  I also have a career that has required significant international and domestic travel for the last 30 years.  On the vast majority of these trips I have been alone. Until recently I ONLY participated while on the road, but that has changed the last few years.  Because of these legit hobbies I use a PO Box to keep my home address private -- in large part because I am a security nut. I make SURE that any applicable credit card bills or (more importantly) airline and hotel reward accounts are registered to my PO Box, also good for security too since a hotel clerk/porter is unable to discern my home address while I am away.  For the occasional times when I need to send or receive $ electronically for my legit hobbies, I have a personal bank account... which can also sometimes be utilized to temporarily hold $ to be used and accessed via ATM if necessary on the road... conveniently in the local currency.  None of this is perfect, I guess, but it's worked well for me

Far from it, I just had to learn the hard way. The ex thought money was just manufactured out of the ATM and didn't take into account that it actually had to come from my bank account.

and need to pay certain expenses in cash.  I doubled my pocket cash when I started this.  I also found anothere place to stash my excess play money besides my wallet or the sock drawer...  yes, there is cash there...  but not my stash.  
Some panels in MY gun safe are removeable.

raise questions. Travel reimbursement checks are a great source of play money.

Well, my wife does all the book-keeping, so it's tough. I set a little aside everytime I  do an ATM withdrawal, and sometimes add 20-40 to a Walmart tab. Tried to set up a separate account, but despite explicit instructions to use a separate addy, corporate at the bank decided to send some stuff on the driver's license ID.  Wifey noticed, confronted me. Managed to talk my way out of it, but had to close the account. So be careful if you do the second account thing

It was my second marriage and we did not mix our businesses, our banking or property. We did have a joint account for bills and the house we lived in was hers.
We are in the process of divorcing and the financial separation is simple.

SO has horrible money management skills or at least had when we had a joint account. Now that we have separate accounts there is way less arguing about money. I think she got her own account on her own with another bank because she didnt want to pay monthly maintenance fees that I never ended up being changed and we just left it that way.

I found out the hard way that using plastic for everything led to overdrafts.  Also, the wife sucked at money management.  So I started withdrawing large amounts of cash to use instead of doing the card thing.  By the time the marriage was going down the toilet, the wife was used to not knowing where every cent went, so it was easy to stash away $20 every week in a hiding spot.  Now I don't need to hide my hobbying activities, but I still set aside that $20 every week.  Sometimes more, if I can afford it.

I funded the hobby with 2nd and 3rd jobs that paid me by check-not direct deposit.  I simply cashed the check and used that.

I have a client who has a own account which no one has access beside him. No trouble from wife.

I have my own consulting job with a business account (for loans, business expenses, etc.) that the wife doesn't/can't look at - it's business.  So, I use that to hide it.  As long as I pay the family - all is good.

If you have kids, you might also set-up a 2nd direct deposit from your payroll into a special account to fund the kids 529 accounts. (Perhaps the next time you get a raise?) Using this separate free savings or checking account guarantees that the account will never be too low to allow the 529 transfer (thus avoiding potential overdraft expenses)... and quietly transfer an extra $100 or more with every check.  Put this account in your name ONLY at a new bank... and NEVER give the new bank your home address!  A PO Box costs less than $40 a year and assures confidentiality. If they need ID when you open your account, show them your passport card with no address.

I'd suggest Macau...