How do i stopped a shared user smuggling someone in the house?

We Love ring doorbell. We have used one so our own home location and also my elderly mother’s. I’ve read a few threads on here and have noticed many of the replies from staff, keep switching to a Ring Alarm device, when people have specifically enquire about the Doorbell..? Our issue is that our youngest daughter has a very shifty boyfriend, who knows how to avoid being detected on the video. How does he do this and more importantly, how do we resolve it? As i can’t figure out a way on the settings. Fyi, this is a Ring 3 (battery). Appreciate Any help as this is stressing out my wife!Gazzapen