When was the last time Oscar was checked at the vets? It's possible he has an infection that needs cleared up. Is he fixed? Not being fixed could also lead to urinating inappropriately. What do you use to clean up after he has urinated or had a BM in the house. If you are using something that just masks the scent but doesn't actually get rid of it he can still smell it so therefore will think it's ok to continue to do this.
Have you thought about crating him while you are at work or at night? That is, of course, after you take him to a vet to make sure it isn't a health problem? Crating is not cruel. It sometimes helps in cases like this.
I am sure people with a lot more experience than me will be along soon to give you some good suggestions. It's been a long time since I've had that problem. Good luck
