I've had my puppy since christmas 08, and he's about 5.5months now... but we're having a difficult time potty training him on the pad. He pee's fine on the pad, but when he goes to poop, he always walks off the pad, and his poo always ends up off the pad. and yes it's better to take him outside, but we got him when he was small, and when winter was around, so we decided to keep him on the pad. any help???