By the time I am 70 yrs old there will be depends a diaper underwear product waiting for me, our bladders just give out or drop, the same with dogs...
Everyone has already gave you excellent suggestions!!!
But, remember a potty trained dog, that all of sudden has incontinence problems, that really upset the little dog, they know they are not suppose to have accidents, it works on them psychologically too...
So maybe at night you can buy those doggie diapers, and use medicated powder or cornstarch....don't use anything that can harm a dog if dog tries to clean by licking...
So sorry your little friend is a senior citizen now and those are hard and challenging times...If, urine just comes our freely then bladder fell and that can be fixed, if its sleep time, set the alarm clock everynight, get pet up and sit to go pee, maybe when younger the pet could hold all night, now can't, so just get up once a night to relieve the pet...
Just suggestions, much luck to you and yours, please give your little friend a hug from me:o)
Try cleaning the are good and put lots of vaseline in that area to barrier the skin from the urine. It's hard when they reach that age and then can't even help themselves go potty. Poor thing! Try making a sling out of a towel, place it under the dogs hind end, waist area and you can help him or her get up. If your dog can't make it up at all I'd get to the vet and discuss quality of life issues. You always have to do what's best for them that's part of being a good dog parent. My thoughts and prayers are with you.
Does the dog have long or short hair? Is he a large or small dog? You might have to shave the parts that become irritated and put cream (preferably something recommended by your vet) on these areas. Our shih tzu is almost three years old and he gets urine on himself during the winter. We had to shave him and put cream on him.
Hope this helps a bit.
lonewolf