Sniffer dogs are notoriously unreliable, often alerting giving false positives etc, they also can only be worked for short periods before their effectiveness drops right off. I've walked right past sniffer dogs heaps of times carrying drugs at festivals and raves and never had an issue, didn't stop me shitting myself every time though and definitely not something I'd recommend anyone does without taking the appropriate precautions, MBB was unheard of back in my misspent raving youth and I've seen many a person hauled off for a pat down and strip search, seems much more full on here in Australia than anything I've seen in other countries including the UK.