Initially mine was not a running-away fund but one for a breast reduction operation once I'd saved enough. DH knew nothing about it as I was too embarrassed to tell him. As the children came along we didn't have enough to save anything at all and by the time I could afford the surgery I was too old to risk the anaesthetic, so it got incorporated into our joint finances.
DH was not useful with money. Not that either of us was at all extravagant, he just wasn't any good at paying bills when they were due or working out whether we had enough from month to month. He was happy to leave the job all to me. Initially we had just a joint account (which I managed till I got fed up of the responsibility, passed the job to him and found us in overdraft within a month!) but when I worked part-time when the children were small I had a separate account. It was needed for my tax return as I was self-employed.
As the years went on we both had self-employed income as well as employed income so three accounts were needed, the joint one for all household expenses.
DH never got to grips with keeping track of money, has not a clue about investing surpluses, and isn't really interested. He is not a big spender (neither am I) in fact he is probably fairly stingy. But he has never objected to any spending that I choose to do cos he knows that I know what I am doing. For example, he was quite happy to live forever with our 40-year-old lounge 3-piece suite and his eyes opened wide when I told him how much the replacement would cost, but he didn't object. I didn't have to ask his permission but I've always given him the chance to object. He never has.
I buy all his clothes, he isn't interested. If I buy him a new sweater he forgets every other sweater he possesses.
I try to keep him informed of our finances, even ask his advice, so in theory he knows what we have in savings, but as he isn't interested he still hasn't got a clue.
If I wanted to run away I could easily take all the money myself, he wouldn't even know where it was.
But I have too many friends and rellies who thought their marriages were secure and found themselves alone and penniless to advise complacency with finances.