Twice a day isn't too much food and that's not what would make him poop that many times a day after 4 years. I'm having this same problem with a foster pup. He was crate trained at 4 months old with no problems, then he started pooping at least 8 times a day, in his crate and outside. Everyone said it was behavioral cause he was a pup. After cleaning crap out of his crate several times a day, we figured it doesn't make sense that behavior could be the cause. A dog's behavior does not give him the urge to poop so much. And he wasn't really gaining much weight even though he is at that lanky puppy stage. So we had a poop sample tested and vua la, he has whip worms. These worms have been very difficult to get rid of too. We've treated him twice with one kind of wormer with no luck and we're on a third treatment with another kind. So take your dog and his poop to be checked by the vet.

He could also be having trouble absorbing his food so if they don't find worms, have a blood test done also.