You can train several target scents, a dog will quite happily handle six or seven different scents, but they will also then find derivatives of those scents. Tiredness can play a factor, particularly at festivals, some promoters are trying to work the dogs teams too long and don’t rotate them enough. It’s quite a boring job for the dog – very repetitive – and the dogs get tired. It also depends on the age of the dogs, temperature of the day, the amount of people coming in, the amount of rest breaks. The dogs will, quite a lot of the time, ignore the smaller scents and go for the bigger scents. If you see the same dog knocking about at the gates all day, chances are they’ve probably mentally checked out for the day. A person might have no drugs on them but may have recently smoked a joint, or that person hasn’t got drugs on them or smoked anything but sat next to someone on the train who is a heavy cannabis user or had cannabis in their pocket, the dog’s nose is so sensitive that they will pick up on it.