Training a senior dog to sleep in a crate or outside?
Middle of the night accidents aren't out of the ordinary for my 15 year old dog. Due to arthritis and general old age, he periodically "leaks" or drops "nuggets" when he's asleep, so cleaning up messes in the morning happens with increasing frequency. I adopted him at 9 years old, and although he was house broken, he didn't seem to have ever seen a crate. Though I initially tried to crate train him, he didn't like it and I didn't push it. He likes spending time in the yard, but not if he knows we're inside, so he barks and paces until he's let in. I have tried diapers and male wraps, but he always manages to get out of them. It's been frustrating, but because he's old I always come up with an excuse for him.
We recently had an incident involving diarrhea that was the last straw for me. I'm tired of regularly spending my mornings cleaning up dog mess. At this point I don't know how to train him to sleep in either a crate or outside as a 15 year old dog that's never had to do it before. I don't want to stress him out by forcing it too quickly, but for my own sanity something has to change.
Does anyone have any advice on how to crate train a senior dog, or how to transition him to spending more time outside? Or any other ideas?
*Edited to remove unnecessary info that made the post too long :)