A side effect of Prednisone or old age?

I have a fourteen yr old lurcher who has been on prednisone for about two years now. For a while he has had problems with pooping on the floor by accident. Poor fellow gets taken by surprise and just cant hold it in, when he needs to go he just cant hold it in. It seems to be getting more and more frequent just lately. Its distressing for both of us, he gets upset cause he's had an accident an i get exhausted cause i'm often up in the early hours clearing up poop. I take him out for a walk twice a day but it doesnt seem to help.