Good luck with the pooping training
or should I say anti-pooping training...
anyway, you've gotten lots of great advice here. I know somewhere someone mentioned food. Consider placing him on a high-quality dog food known for producing small stools.
I know it sounds nuts, but my Bernie is incontinent (both urinary and bowel) as a result of being run over by a car (before I gotg him) My vet had us switch him to a senior food (I've since switched him to Pinnacle Trout, which isn't a senior food but works very well) and he hasn't had to wear diapers in the house for ages!
Actually, I thought he was cured. Then the store where I buy their dogfood was OUT and I had to give him something else for a day or too. All I can say is, "watch out for flying poo!".
So, he is apparently still semi-incontinent (there's definitely no control when it flies...trust me) but on this food can control it.
Anyway, MY POINT IS, it creates smaller, less frequent stools...that may help too.