"Canines are taught to detect concealed U.S. currency and firearms. Both the Officer/Agent and canine are taught the proper search sequences when searching vehicles, aircraft, freight, luggage, mail, passengers and premises."
I have no idea what the ratio of scientific backing vs. security theater is, though.
[0] https://www.cbsnews.com/minnesota/news/golden-valleys-new-k-...
[1] https://www.akc.org/expert-advice/news/meet-currency-detecto...
[2] https://www.cbp.gov/border-security/along-us-borders/canine-...
Yes, dogs give you a convenient excuse to produce 'probable cause' in order to authorise a search whenever you feel like it, because the signs the dogs give are interpreted by their handlers.
So it's not necessarily so much security theatre, as perhaps 'whitewashing' of evidence obtained in other ways. see eg https://en.wikipedia.org/wiki/Parallel_construction
That said, no one on the Internet knows that I am a dog.
https://www.akc.org/expert-advice/news/meet-currency-detecto...
From the concept of "they'll only do that once, and probably be useless the rest of the day". ;)
During a three-week period, fishermen fooled the Nazis and police dogs who
searched their ships – lacing handkerchiefs with a mixture of rabbit blood and
cocaine, in order to fool the dogs.