Mia, Luke and Corinne were trained in tracking (not cadaver odour detection as was suggested in an earlier post) by an ex-army dog trainer with over 20 years' experience. His name has never been in the public domain, therefore I will not name him (just as I've never named the male family member said by John Ferris to have been in Alice Walker's house when, Ferris claimed, Alice and this other family member told Ferris not to go to the police).
The police knew who the trainer was and had already spoken extensively to him prior to Luke's Section 14 interrogation, since they made several references to him (the trainer) by name and to the techniques used in the tracker training process during that interrogation.
The written training records were taken by the police and made available to both the prosecution and the defence. The defence expert tested Mia against the information in the training records and wrote a report saying that the information was accurate - Mia had been trained to that standard. When the defence asked to bring the expert to court as a witness, a decision was taken that Legal Aid had already paid for the report, so the defence could cross examine the crown experts on the basis of the report, rather than incur the cost of having the expert attend personally to give evidence.
That's not unusual (and it certainly wasn't unusual in 2004/5) - defence teams are often refused funding to bring experts in at trial if they've already been funded to provide a report, on the basis that the defence has all the information it needs, from the report, to address any claims the prosecution might make. It's clearly a biased decision making process, since it requires lawyers to identify any failings in the prosecution experts' evidence (and often, these are couched in extremely technical language relevant only to that expert's discipline) and then figure out how to counter that with information from their own expert report.
An argument a few years ago, suggesting judges should become "gatekeepers" to ensure claims made by forensic experts were adequately supported by science, collapsed on the basis that judges are experts in law, not forensic science.
However, there's another question relating to the Yorkshire dogs (the ones brought in after the scene was bleached) that's never really been addressed. Why did the police bring in cadaver dogs, rather than tracker dogs, 12 days after the murder? Jodi's body was removed from the scene with 17 hours, at most, of her death. Had the dogs been following the "scent of death" (as it's been described in some articles), one would have expected all of them to have headed in the same direction - north, across the woodland strip to the barbed wire fence over which Jodi's body was passed to be placed in the ambulance on the morning of July 1st.
If they were searching out the scent of decomposing blood, deposited by "the killer," how would the dogs differentiate between blood transferred by officers who entered and left the scene in the early hours of the morning and blood deposited by the killer? What about anyone else in the woodland strip whose shoes may have (unknown to them) become contaminated with Jodi's blood - Alice Walker, who touched Jodi's body, James Falconer, David Dickie, the kids playing in the woodland strip, etc?
If Luke was the killer and left deposits of Jodi's blood in the direction of Newbattle earlier in the evening, he would also potentially have carried deposits of blood (or cadaver odour) in the opposite direction later that night, after the finding of Jodi's body, since he, like Alice and Steven Kelly, was over the wall. We know there were a number of places where traces of Jodi's blood were found - anyone walking in the area could have picked up those traces and transferred them elsewhere.
Any officer over the wall in the early hours who walked towards the Newbattle end of the path (to put up cordons etc) would also have carried cadaver odour in that direction - how would the dogs have known which was a deposit from a police officer and which was a deposit from a potential killer?
And, of course, all of this was based on the killer escaping towards Newbattle, for which there was, at the time, not a single credible piece of evidence. And the whole thing was rendered pointless by the bleaching of the scene before the dog got there.
But why cadaver dogs in the first place?