As for sniffers finding these things...the signals are already being lost in the noise. Dogs can find certain kinds of explosives, but are fooled by others. And the vapor emissions can be very, very low. (Nothing is ever "zero" on a log scale, of course, but something sealed inside a glass ampoule and very thoroughly rinsed with water and alcohol and benzene and such is about as close to "no emissions" as one can imagine.)
Sniffers are one way to detect things, but as you point out, it is possible to get emissions so low that they cannot be detected. However, the new methods are based on other exotic things like neutron scanning and mass spec, which can detect chemical composition, right? Also things like CAT scan X-rays and maybe even ultrasound can detect different material types; ie, bone and flesh look different, so perhaps C4 has a different X-ray opacity than other things? With things like neutron scanning, it should be possible to detect stuff anywhere in the body, perhaps? That's why boobs are the perfect place for this. A big homogenous-opacity shape in a body cavity or the abdomen is suspicious, but boob implants are "normal". I know little or nothing about these things. Maybe someone can give us a summary of the different super-scanning technologies? Even without knowing anything about them, I do know that they will all be expensive, and, even if they are safe, they will have to overcome public perceptions about radiation. And brand-new technologies like this are usually only partially effective. Interesting stuff. At the beginning of the 20th Century, four countries had the opportunity to become empires: The US, the Russians, the Germans and the Japanese. After much bloodshed, the US won (I'm glad about that, especially when you look at the alternatives). Now the US is having to put up with some of the unpleasant aspects of being an empire, and that's why we're even discussing neutron scanning to detect explosive boobs (aka "booby traps").