I have also repeatedly wondered about the reliability of sniffer dogs, but I also know little about them. I'm not sure what they would/not have picked up in the yard and contaminated areas closer to the house: William's scent PLUS that of heaps of others', or just a mix of everything all in one. Also wonder whether, as someone else pondered, whether a child emits less scent than an adult. Also wondered whether the scent may have been 'blocked' by something, like if William was wedged under a huge boulder or something...
I think back to the David Iredale search in the Blue Mtns in late 2006 - can't recall if they used dogs or not - but many people were searching but he was under some boulder and it later transpired that many people had walked past that place many times...
But, it's not like they did just one search in the bush for William. Not sure how many times they took the dogs in, but msm has reported that some places were searched up to ten times!
The police keep saying they reckon they would have found him, if he were in the bush. But they are also going to go back and do intermittent sweeps of the area around Benaroon Drive... I wonder what that's all about?