IMO we can't assume that search and rescue dogs will always be able to follow a wandered child's scent - it depends greatly on the conditions.
For example tracker dogs did not manage to track the route 2-yr old Baby Rainn walked.
And tracker dogs did not manage to track the route 2-yr old Issac Leuenberger walked.
Deorr was wearing large wellingtons, pyjama bottoms which must have been tucked inside the boots and also a long-sleeved jacket so virtually the only skin cells being deposited would have been from his head.
Isaac Leuenberger had covered a few kilometres before he was finally found.
The search for Rainn was hindered by waist-deep grass - I suppose it depends if the dogs were air-scenting or ground tracking trained.
The searches for Deorr have been so extensive over a long period of time, I don't understand why they haven't found him if he merely wandered. However, the apparent discovery of a jacket & the cars opens up a real can of worms. Someone close may have been trying to set Jessica & Vernal up.