eater81 - Even if a dog sniffs you and detects something, I don't think the police have rights to search you or ask you to empty your pockets. I might be wrong on this though - but I think you CAN refuse for a dog to sniff you - since they would need reasonable grounds for suspicion to use one on you in the first place. It's rather invasive of them to use a narrow alleyway to do this though. Most of the time you can actually say "no" to the police, but most people don't know their rights. Just like the police have no right to enter your premises without a search warrant. Unfortunately, new terrorism bills are stripping us of these freedoms though.