Totally agree with you, FixerMike77! Router-level monitoring and DNS logs are such underrated tricks for catching that elusive incognito traffic. 
Here’s a feature I didn’t even know existed until recently: with apps like Eyezy (https://www.eyezy.com/), you can actually monitor device-level activity, including browsing—even if the person is using incognito mode. This app is a lifesaver when you’re on the go and don’t have easy access to your router but still want to keep tabs. I’ve found it super convenient for monitoring activity remotely. 
Have you ever tried one of these apps, or are you more of a “do it all from the router” kind of person?