The rats, the dogs, the bears, all macrosmatic critters can smell 'in stereo'. The whole olfactory system is basically two bilaterally symmetrical mirror image systems. It is what allows the critter to discern the direction the scents coming from.
It is not that the jackals ability have been discredited, but science has simple shown a bigger dog equals more OSNs...More OSNs equal better ability.
The Border terriers you mentioned are kinda like the half jackals, first their abilities are so far above ours , and just barely below a full sized dog...what they lack in OSNs they make up for in drive. Its why Jack Russels are such good hunters, and Ive even seen dachshunds used for drug detection in facilities. Even the so called push-faced dogs whose olfactory systems are really screwed up, smell so much better than a human that it is hard to grasp.
Since you are in the UK a common dog for EOD over there ( bombs) is a Springer Spaniel. Again a little smaller dog, but with a little bigger 'drive'
They are excellent at their jobs.Our Dept. Of Agriculture uses beagles for a similar reason, they are good at what they do and are deployed in public places, where no one finds them intimidating. I had one indicate on a bottle of Ms Balls Chutney-new,sealed and unopened- in my luggage like Id just poured it out in a bowl....( It is processed fruit and therefore OK to bring in...)
