Old dog having accidents

Shadow is 15 yrs old next month, he is becoming a bit unstable on his back legs but manages to get a round still, he's all there in his mind, still likes his food, and treats, for the last 4 months he has been pooping either on his bed or in kitchen during the night, baring in mind my daughter goes to bed at 2 am lets him out before retiring, then we're up at 6am, we thought he can't control holding it in anymore for a long period of time, but this afternoon I witnessed him lying on his bed wide a wake his tail goes up and he's pooping on his bed, now is he starting to be lazy or is it he has no control over his actions?:

I doubt very much he is being lazy, a dog wont generally eliminate in their beds. The poor old soul is probably quite distressed about it. 15 is a ripe old age, is he a large or small breed?

He's a golden Retriever, I always said the time will come if his legs go or he has no control over his bodily functions, but his mind is still sound and he is still happy, people say you know when the time comes, and I don't think I've seen it yet!

My last Oldie used to do this. He didn`t really know it was happening. I think a few times he was actually asleep (old dogs sleep so soundly). He had Spondylosis, and I think had lost a lot of feeling in one of his rear legs - and I assume his back end as well.
We got into the habit of making sure he`d gone out for a potter round at intervals, rather than leaving it up to him, and that worked quite well.