Quite Easily -
Transparency is key -
We agreed on a set amount that automatically goes into an account I created. I also have a PayPal account that I use. Those two are mine, and no one's to touch. This way she never sees the money, she doesn't know it's missing. If I need more, we talk about it and most times she will loan me until the funds I need in lieu of a hiatus on auto transfers until the money is repaid - this eliminated cash flow issues when I wanted to do something. My wife will also do the same for me if she needs something and I can assist. It also scores HUGE brownie points when xmas/bday gifts come from that account - makes the money untouchable
Good logic and communication always wins!