I would just do it out side to be honest. Cats dig and somewhat cover their mess with litter when they are done, a dog would most likely just leave it sitting at the top if you could persuade it to go in a litter box to start with. Pee pads are for pee but a dog can poop on it too, just huck it out when its soiled and put down a new one. To potty train a puppy just try to get it going outside ever...4 hours or so on a leash and keep it out there untill it does its business, even if that means waiting for 10-20+ mins, praise it after its done so. if you catch it doing its business inside, clap your hands and try to get it to stop or lift it onto the pee pad(which should be by the door) ...that's how we did it with the five or so dogs we've had growing up, only thing i must stress is DO NOT rub your dogs nose in an accident and yell at and or hit it, it scares them and makes the potty training process last longer