A recent blog referenced a SCOTUS decision where a drug dog sniffed out marijuana in a man's car, initiating a search. SCOTUS determined the search was legal.
This article isn't about the rightness or wrongness of the search. I have my own feelings, you likely have yours. It is, however, about the fact that such searches are consistent with application of the law in the US for some time.
About two years ago, I gave a friend of mine a ride to pick up his children from the boys and girls club. When we returned to his house, we remained in the van chatting as we were in the midst of an involved conversation. After about 10 minutes, a police car pulled up behind us. They asked to see my driver's license, which I provided, then asked to search the van.
While I am a privacy advocate, I also know they have the authority to hold me for up to 48 hours with no cause whatsoever, longer if they can use the "material witness" exception. So, I let them search.
They turned up nothing, of course, but did state suspicion over a set of kitchen knives that I had in the middle of a bunch of flea market items (potential weapons, you know). They let me go, and I spoke with the head of the department the following morning. While he understood my concerns, he did remind me that operating a vehicle on a public street subjects one to "consent searches". You can, of course, deny, and refuse the officers the right to search, but it could result in your being held for 48 hours so they can more thoroughly check your background.
In other words, you CAN exercise your rights...but they can make it mighty miserable on you if you do.