A Newfoundland puppy is easy enough to housetrain, but you have to teach him the right way from the beginning.
A Newfoundland puppy is an extremely intelligent dog and will understand what is required of him if the right approach is used.
The first thing to learn is the way that dogs think. They learn by association. It is no use yelling at him after he has gone in the wrong place - it is too late by then and he will associate your presence with being scolded. He has no idea what he is supposed to have done and showing him will not improve that situation.
All he will know is that you come home and he gets shouted at. So, do you want your Newfoundland puppy to come and greet you with his tail wagging? Or do you want him to run away and hide as soon as he hears you coming?
You need to watch him carefully, look for signs that he is sniffing around, looking for a place to go. As soon as you see this, you must pick him up and take him outside into the garden. Do not just leave him out there - he will forget about going and want to follow you inside. You need to stay with him, wait for him to go no matter how long it takes. You can associate a word with this, as soon as he performs, but not until.
You should also take him outside after he has eaten and when he wakes up. Puppies will toilet a lot. It is hard work keeping up with them, but it will not take long provided that you pay attention to every little move he makes.
Once he has toileted where he is supposed to give him lots and lots of praise and treats, then let him back inside.
What if he starts to go in the house? You simply pick him up and take him outside, even if it is too late and say nothing. He will not understand if you scold him for going in the house; he will think he is being scolded for doing what he must do. The result of this will be that he will either find somewhere to go where you cannot see him, or he will wait until you are out of the room.
In his mind, he gets scolded if you are there; he does not get scolded if you are not there, and you will have forfeited your chance to praise him for going in the right place. No way is he going to perform with you hanging about!
If he does toilet in the house, and it will happen on occasion, be sure to clean it thoroughly with a biological washing powder or one of the many products available from pet stores. If the smell still lingers, he is more likely to go in that spot again.
I managed to housetrain Ferdie in two days, but he was a little older at 13 weeks. We still had accidents at night of course, but they were always beside the back door, proving that he was first waiting for someone to let him outside.
It is a good idea to remove rugs and cover carpet with heavy plastic sheeting. This is easier to clean and will ensure that the smell does not linger.