Can an old Dachshund change his walking pattern

My husband's elderly father has recently undergone surgery and can no longer walk his dachshund. This dog is older and is on a 4 walk a day schedule. I want to fence in the yard and put in a doggie door so the dog can go out when he wants to. My father-in-law adamantly believes he will only go to the bathroom when he is walked. Is this true with this breed of dog? Can you teach an old dog to change his routine?