[Treeve]

How do you prove if they drove over the border one night and came back?

You don't... it's in the 'normally garaged' part of the statement. If they have proof (such as you having a nsw license, or a job and place of residence in this state even though you have a vic license, then you are normally in this state.

In fact, in the above paragraph if you're on an interstate license for more than 3 months you're then considered not licensed too, so it just gets worse. They have ways of proving this kind of stuff - not all govt departments are as slow as you may think!