Police dogs have been called in to patrol South Australian rail yards after a Melbourne group’s failed attempt to flee Victoria on a Perth-bound freight train.

The dogs will join Australian Defence Force personnel at checkpoints from today, with South Australia Police Commissioner Grant Stevens saying other freight train stowaways had been busted since the Victorian border closed.

“This sends a strong message to anyone thinking about sneaking across the border that they will be caught,” he said.

“Police can and will be issuing expiation notices up to $1,000 for anyone found to be breaching border restrictions.

“They will then be placed in quarantine, and removed from South Australia as quickly as possible.”

Four men who tried to sneak out of Victoria faced $20,000 in fines for breaching COVID-19 restrictions, but walked away from court on Wednesday afternoon without penalty.

The men aged 22, 26, 29 and 29 tested negative to the virus and were escorted by police to Adelaide Airport on Thursday for extradition on a flight back to Melbourne.

In court, they claimed they did not know about South Australia’s border restrictions.

The train they were busted on departed Melbourne about 10.30pm on Tuesday.

They spotted on-board the train at Adelaide Freight Terminal at Regency Park on Wednesday morning.

Dog operations will begin at the checkpoint near Renmark and travel to other border checkpoints during the week.

Police will also monitor trains as they pass through the state.