[Quiet Man Cometh]

That's mean to the poor doggy! Maybe you could make a little turf box for him? It worked for my sister's mastff after she had puppies and the stairs were difficult for her. Put some turf in a box on the upper landing of the porch but a small box could be put inside. At least somewhere so the dog feels like it has a spot to go instead of stressing all the time. Most dogs I know don't like having to poo inside if they can avoid it. They know it's bad and stresses them out.