I have a male lab mix and he's appx. 15 years old. In the past year he has started to pee and poop on the patio. And its not like he can't make it to the grass because he walks to the edge of the patio and does his job. He doesn't do it all the time but often enough. I cleaned the patio with bleach once and one time with ammonia neither solution worked because with in 24 hours he was doing it again. Mind you he did poop in the grass and I even saw him pee in the grass. What can I do? I've thrown his poop in the grass and said "thats where you go". Short of walking him to the yard and watching him go we've tried about everything. I refuse to believe its because he's old because he does go in the grass to. What can I do to end this habit??
Thanks for any suggestions!!

Just because he makes it to the grass at times doesn't mean that he doesn't have problems holding it in.

The time between outings and when he was fed or watered last can affect how much he needs to go. How far he makes it can also depend on arthritis and other age related disorders. Like with humans the symptoms can come and go-good days and bad days.