Coolio said:
It doesn't matter how well a dog's sense of smell is. A vacuum sealed plastic bag will not let any particles in and out of it, and smells require physical particles to travel through the air to the nose doing the smelling.
Irrespective of whether the seal is absolutely perfect or not, plastics used in bags are permeable to many organic compounds. A physical chemist could describe the details much better than I, but the net result is that plastic bags "breathe" a certain amount of certain molecules that are contained therein.
This permeability varies based on the type (and thickness) of the bags in question, but I don't know that any bag of a reasonable thickness is 100% impermeable. Vacuum sealing, thus, does a good job of cutting down on the smell of stuff but doesn't eliminate it entirely.
Beyond permeability, the biggest mistake folks make when sealing packages is handling the outside of the package with hands or other objects that are contaminated with the substance. Even washing the bag won't remove those contaminants entirely, so they are easy for a canine to smell no matter the stuff sealed inside.
To me, it's always surprising how little folks appreciate the canine nose. We, as humans, basically "think with our eyes" (see Crick's
The Astonishing Hypothesis), neurologically speaking. Our canine friends think with their noses - the world is a world of smells to them. In comparison, our human noses are essentially vestigial organs - still marginally functional, but nothing like the fully-functioning canine nose. I've seen all sorts of hare-brained stunts to try to get around drug-sniffing dogs, and 99% of them are pointless. In particular, masking agents to "cover up" drug smells are all but hopeless - think of it as trying to "cover up" a bright pinprick of light in a dark room by shining some other-colored lights into the room. . . it's not going to work, it'll just result in a few different smells that, to a dog, are easy to decouple.
As to the comment above about a compound that will "prevent dogs from smellin female dogs letting off heat," no such thing exists (by the way, female canine are "in heat" when they are cycling, i.e. in estrous. . . they don't "let off heat"). Anyone with experience handling stud dogs in a breeding program well knows that no masking agent on Earth will block his ability to smell a bitch in season, period. Now, there are compounds that mimic the smell of bitches in estrous (including coyote urine) and I've had folks ask if they could be used to foil drug dogs. My answer (without testing, mind you) is nope: first, not all drug dogs are males - and those that are generally are castrated; second, even non-castrated males are easily trained to ignore a bitch in heat while doing a job (perhaps not perfectly, but well enough to be effective - boys can be professionals when the need arises); third, this is just a form of "masking agent" that is designed to confuse or distract the dog - it doesn't do anything to prevent him/her from smelling the drug-related compounds in the first place.
I know someone who regularly brought two of his non-castrated males with him on smuggling runs, with the knowledge that a positive indication from a sniffing dog could be questioned on the basis of having two other canines in the vehicle - I don't know that legal theory has been tested in court, but it's better than nothing. The person in question eventually got caught, but he negotiated a very good plea deal. . . perhaps some of that negotiation was based on the presence of his two boys?
There's talk of using sneezing powder to hold off sniffing dogs. . . I think it'd work, but the sneezing would be suspicious enough by itself and one might pull a new charge if they LEOs got mad. The powder isn't dangerous (to dogs or people), but one never knows - plus the whole "scary white powder" issue would likely pull a massive terrorism response. . . not ideal.
I do know of some compounds that actually work to completely thwart sniffing dogs - they are still deep in the research field, and I'm not even going to mention the academic area in this post. I've not bothered to get ahold of them, as I'm out of the game nowadays, but if I were still running dirty I'd certainly be looking into them. Only someone with a lifetime's fluency in veterinary topics would be barking up the right tree in finding these compounds, however, which means not many wholesale narcotics couriers are going to fit the bill.
Peace,
Fausty
ps: the sad fact is that drug dogs are
really trained to indicate on command as much as they are trained to find drugs. Even a dog-ignorant fool can get a dog to wag his/her tail by talking excitedly and tapping in one place. . . they whole thing has turned into a farce meant only to evade Constitutional protections against unreasonable searches.