[Osem]

UK airport security staff do check for large amounts of currency and have dogs trained for the purpose. They certainly check for people trying to get money out of the country and if they can't prove it's legit they confiscate it and have to prove entitlement in court IIRC. I presume they do the same for incoming passengers. I'd have thought it'd be even tougher in the US but possibly not so for internal flights.