Hypothetical scenarios here, but trying to keep them based on reasonable logic:
If someone was interested in inquiring about the prospect of work on the property, when would they likely turn up?
I would have thought the end of the working day would be logical - more likely someone there at the homestead. Would a Saturday or Sunday be more likely, given potential other commitments the person may have? Would choosing AFL Grand Final day make some sense, with the expectation that at least someone may have watched it and therefore be at the homestead (waiting until the game had finished, so as not to interrupt)?
Could such a person have already worked at the property in some other capacity, and have a knowledge of the dynamics? Josh not present, so maybe the need for some male assistance? Could be known to both Gus and the dogs? Could he have potentially parked at the gate, knowing it was only a 300 metre walk to the house?
What if such a person turning up, coincided with Gus having wandered down the driveway, even a short distance?
Would it make sense that Gus would walk on an established pathway/driveway, rather than wander aimlessly into the scrub? Could he have seen or heard a car pull up at the gate, and assumed it was mum and went to meet her?
Once the alarm went up, you would imagine the driveway would have been one of the first places of interest to search. That would have meant footprints everywhere, if the ground surface was receptive. That would make distinguishing individual footprints very difficult. Alternatively, the ground wasn't receptive to footprints, or the conditions meant that they were erased by the next morning.
Would tyre tracks leading up to the gate be distinguishable in the above scenario?
Who knows, but a number of other vehicles probably drove the same route before anyone had a chance to check.
If the person was carrying a phone, would it be detectable?
Probably, but to what extent? A mobile phone solved the Cleo Smith case relatively quickly, but only because she was present when the police first visited the owner of the phone. Russell Hill's mobile phone was the key to linking Greg Lynn to that crime, but it took over a year for the full diagnostic analysis to be completed. The police told no-one about the phone, including Russell's family.
It is still quite possible that Gus wandered beyond the search zone, but hearing nothing from police doesn't rule out a potential Greg Lynn-type situation. If there has been foul play, there is simply no advantage in police giving the offender a heads up.