The farmer pinned a new badge onto Spike's collar strap. It was shaped like a gate.

"You three are the Biosecurity Team this week," she said. "Your job is to keep germs, weeds and pests from getting onto our farm."

Little Thunder puffed out his chest. "Nothing gets past us."

The first visitor was the vet. Suzy checked the list. "Clean boots, please." The vet smiled and scrubbed her boots in the footbath by the gate.

Next came a truck delivering three new cows: Lima, Oslo and Cairo. "New animals stay in the quarantine paddock for a while," Spike explained, "so we can make sure they're healthy before they meet the herd."

Oslo nodded. "That's sensible. We don't want to share any sniffles."

Then a hiker wandered up with seeds stuck to her socks. Little Thunder spotted them first. "Those could be weed seeds! Could you brush them off into this bag?" The hiker thanked him and cleaned her socks carefully.

In the afternoon, a neighbour's ute arrived covered in mud from another farm. Suzy pointed to the wash-down area. "Mud can carry weed seeds and germs. A quick wash keeps everyone safe."

By evening, the friends sat by the gate, tired but proud. They had stopped mud, seeds and germs, and they had done it politely.

"Biosecurity isn't about saying no," said Spike. "It's about saying yes, safely."

The farmer came by and smiled. "Australia's farms are protected by people who care at every gate," she said. "Today, that was you."

Little Thunder gazed across the healthy green paddocks. "Best job on the farm," he said.