The mystery of our night time visitor has been solved. After many months of finding holes that had been dug all over the garden, and after much discussion as to what was doing it we decided to set up a night time nature camera.
Was it a possum, a bandicoot, an echidna or some other creature. Well the nature camera was set up. Many nights it eluded us, either nothing or just the local cat walking by. It was still around as it was digging in other parts of the garden.
Then hey presto we have it, a bandicoot. It is doing a great job getting all the undesirable bugs out of the veggie beds and turning them over for us.