Sounds to me like you have bigger issues than $100 when you have to hide from your wife ordering detailing supplies or mods for your car and have to ask her first. Sorry, but I'm just saying it like it is. My wife never questions how I spend the money I earn. We also have had separate checking accounts since day one of our "26" year marriage. When I bought my GC I was like, honey I'm buying a third car will you drive me to the dealership to pick it up. Oh and buy the way, check out these new wheels and how awesome is this new custom exhaust I just bought LOL. She never said how much or why didn't you ask me or where did you get the money.
I'm sorry you have to go through that and make up stories to justify your hobbies. Makes me realize how good I have it, I'm going to go hug my wife and tell her how much I love her and how great she is. I just know I could never live that way.
On the flip side, if I kept my money separate I'd feel like I have a roommate, not a wife. Why keep it separate anyway, it's all communal. Our paychecks go into the same account, sounds like one of you has money trust issues. Sorry, I'm just saying it like it is.