Read through the sticky on housebreaking including the the part at the end on older dogs at
http://www.askmehelpdesk.com/dogs/in...tml#post251809 You could try putting an old towel outside and see if he will use it. The grid I suggest in the sticky helps on urination, but less so with stools.
He may do better if he accepts you being in charge. The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at
Raising Your Dog with the Monks of New Skete For more on being top dog, see
Establishing and Keeping Alpha Position, Letting your dog know you are the boss