How do you manage distractions from others (spouse, kids) when deep in focus?

I wfh 2 days a week, along with my wife. She has a very different work schedule and style than me (she’s in marketing, I do data science) and I work best in sessions of deep concentrated states, whereas she’s more free flowing and can just pop in and out of working better.

My current approach of headphones in doors closed doesn’t always communicate that “even a knock / quick question will throw off my flow”. Often times it’s just a quick question and the focus is gone for me.

Curious what works for other people – a system, signal or conversation that established when is absolute ‘lock in mode’ vs. when it’s okay to come in? Or is this just the tax of working from home with others around?