Oh another thing I like about this system, is that its completely unique, Harley actually doesn't know that he has the option to pee on grass. Sometimes he'll poo on a walk on the concrete, but he never pees when we're out. it's great for us cause we do agility and you get eliminated if your dog uses the bathroom on the course.
Also make sure that even if you keep him as an "inside dog" that he get plenty of exercise, and walks. Luckily with these guys they are small enough to exercise inside in inclement weather, but they really do enjoy walks outside and interacting with other dogs.