When he does have an accident, are you scolding at all? Scolding doesn't mean you have to yell or rub their nose in the mess. You can still go "NOO! OUTSIDE!" And clap your hands or something to distract him. When you do catch him going outside successfuly, praise like your puppy just won you the lottery. I am sure you are doing this already though :p
You are doing a lot of very good things and keep it up! I am having potty training ups and downs withy my 10 month old. She was tough to break at first because she had a UTI that I didn't have her tested for until 5 or 6 months of age - after medication I thought she was potty trained! Nope. I later found out that she was resoiling over old spots, behind the couch. Since then I have gated off her access to the areas she has accidents in.
If he is still having pretty frequent accidents, then I would go ahead and reduce his amount of den space.
I think Karlin is right, a lot of it is just that potty training happens as they get older and as long as we are very patient and consistent with them.
It seems to take FOREVER for them to finally communicate when they have to go out. I can't remember the magic age; maybe nine or ten months. We tried for a long time to get her to use bells hung by the door, but all of a sudden she decided to bark to get our attention. Thank goodness, because we were getting sick and tired of cleaning up after her. Once during a dinner party she peed on a chair in front of everyone because she wasn't getting the attention she was accustomed to. My guests were dumbfounded, their eyes and mouths wide open staring at her, and I heard someone say, OMG, you have to ignore her!