From the beginning of creation, dogs were made to have jobs. Ninety five percent of dogs all around the world were originally work breeds. Only five percent were bred to be lapdogs. But in modern day Australia we don't have legitimate work for dogs to do unless they are on the farm. Therefore the walk is the most important job you can give a dog. Even if you have a big back yard for your dog to enjoy it's no substitute for a good long dog walk with you or a dog walker who will provide plenty of exercise.
After a long walk your dog will go into resting mode so you can feel comfortable about leaving her and letting her sleep it off.