so we can take him out every 3 hours or so.
Hi Carole, I know you must feel frustrated, but this "problem" is fixable.
First, you should take Cubby outside every 30 minutes
, even if he went just 30 minutes ago. Take him outside and give him 2 to 3 minutes to go (it should not be playtime). If he doesn't go, take him back inside. If he does go, praise lavishly and reward with his favorite treat! REPEAT AGAIN IN 30 MINUTE INTERVALS UNTIL BEDTIME.
Second, put him in an exercise pen with a plastic tarp on the floor to make clean up of accidents easy when he is in the house. Don't give him to much freedom when he is this age and not house broken yet.
Third, he is not marking, but he is being stimulated by the smell of urine from his previous accidents in the house. Nothing makes a dog more stimulated than the smell of his urine or another dog's urine. There are products you can use that will minimize the smell of urine inside the house that you use to clean up accidents. The more he goes outside, the more he will be stimulated by previous potties outside and he will want to go there.
We live just down the road from you and we are available for some "hands on" help if desired.