So, you want to keep him tethered, so it's easier to tell when it's potty time?
If you take him out and he doesn't go potty, you can keep him tethered to you (or keep him somewhere where you can have an eye on him) and take him out again in an hour or so. Maybe that'll work.
Bella has learned that when she goes to the door, I take her out. Sometimes she'll go back to the door right after we come back in...because she wants to play outside. I don't want to discourage her from going to the door (because it's a good thing!) but man that's annoying.
To to be honest, I probably take out Bella too frequently. I get nervous after a few hours and I want to avoid accidents, so I don't think we go longer than 3 or maybe 4 hours when I'm home with her. She should be able to hold it for 5 hours at this point (4.5 months old).
So, does Chubbs hold it when you're gone all day? At first, I was leaving Bella in her crate when I went to work AND during the night. Like you, I felt awful. So, I started letting her sleep in the bed with me and I started taking her to daycare while I work.