Jesus, I thought the whole coffee/sniffer dog crap had settled down until I saw this thread :0
It's been said time and time again by cops, druggos and a thousand other people - coffee and other strong-smelling substances designed to confuse or overwhelm a narcotics detector dog simply do not work.
Dog's have a very accute sense of smell, much different to humans. One good example is this; "When humans smell a curry, they smell the curry as a whole. It is not until they look with their eyes that they are able to accurately distinguish the contents of the curry. When a dog smells, they smell the individual components of the curry seperately, just like they do when they smell drugs."
There are some instances where Activated charcoal has had some success, but the dog's reaction to the charcoal is very obvious to the dog handler, and is something the handler will be looking for. Coffee simply doesn't work at all, if anything it is working against you by providing the strong smell that humans can pick up on.
Animal pheremones and perhaps "dummy" plantings of illegal drugs are about the only things that will help you against a drug sniffing dog. Pheremones certainly have some potential, as the right pheremone can render a dog distracted and useless for sniffing out the good stuff.
"Dummy" plantings are also another possible solution, although this is of limited use outside of a house or vehicle. if you know you will be subject to drug sniffing dogs, plant VERY (ie can barely be seen by the human eye) small amounts of your drug around your stash area. This will send the dog into a frenzy with all the scents of the drugs and as long as the dog doesn't go straight for your main set, the handler should lose faith in the dog and call it a day.