The key method to adopt here is one of positive reinforcement. Firstly, you need to show your pup the area where it should do its business, and each time the pup toilets in the designated area, immediately reward with a treat or verbal praise. In order to prevent mistakes from happening, it is important to both diligently supervise your dog while it is indoors and take it frequently outdoors. This will speed the learning process and prevent any accidents from occurring in the house.
It is important to note however that dogs who are never, or seldom allowed indoors, are more likely to become bored - and as a result become disruptive (e.g. bark for attention) and/or destructive (e.g. dig up your newly- planted rose bush). This is because dogs associate their human family as their pack and can develop behavioural issues if they feel neglected as a consequence of being excluded from interacting with their pack.
As a dog owner you are fully and legally responsible for any harm or damages caused by your dog. If your dog bites a human, kills wildlife, damages property, causes a traffic accident, creates noise or other pollution, or is the direct cause of any other damage to the community, you may have to shoulder a substantial financial (if not legal) penalty. It is in your best interest then to always keep a vigilant eye on your dog in public and provide him with the obedience training and socialisation skills necessary to become a well-mannered and socially well-adjusted dog.
Lungworm larvae may be present in slugs and snails, and if eaten, pets may be infected with worms that make their way to the lungs, where they block airways and make breathing difficult. Most dog wormers don't claim to treat lungworm, although some cat wormers do. Research conducted internationally has found moxidectin, which is found in some heartworm treatments for dogs, to be effective against lungworm, but this claim can't be made for dogs on packaging in Australia. Check with your vet as to whether it's an issue in your area, and discuss the best preventative treatment.