Need to train old dog to use puppy pads in middle-of-night

What?First what’s the preferred grammatical way of phrasing that, because what I just wrote implies that I need to train him in the middle of the night. Though, perhaps I do have to train him in the middle of the night? The problem is, I don’t want him to get used to just using the puppy pads whenever he needs to go. Though, perhaps, I do?

Herman can’t hold his bladder. Yes, this reminds me of a certain cat I used to have. I couldn’t train him, but he was a cat, after all.