My 16 year old border collie mix recently started to poop in the house... usually its right after he has been outside... He appears to want to go outside more often. I am home so that is possible. Is this old age syndrome.. or dementia? He can't hear well, and has cataracts, but otherwise is lively. And understands sign language. I did't punish him for the accidents because he is such a good dog and behaves well... until now.