Dog Pees in House When I Get Home Later?

I recently moved with my dog. He used to have access to outdoors and indoors all day though a doggy door. The new house does not have this. However, he is only ever home 4.5 hours without a potty break. Either I go home at lunch or a dog walker comes and takes him to the dog park. He was doing fine. However, recently I started a fitness class after work which brings me home an hour later. We adjusted his potty break so the dog walker comes at noon (I leave at 8:00 a.m.) and leaves him at 1:15 p.m.

and I arrive home at 5:30. He has been peeing on these days I have this class only. He is home alone the same amount of time the other days, but does not pee when I am home at the usual time, even though the times he is alone are the same. I wonder if he is doing this just because I am not home when "I am supposed to be"? How can I break this habit?

By Jenna