A Liberal Party plan to have police conduct random drug checks at South Australian schools is a policy the Police Commissioner has not asked for and principals do not want, according to the state's Police Minister.

Key points: SA Opposition Leader vows to introduce random school drug checks if elected Premier

SA Opposition Leader vows to introduce random school drug checks if elected Premier Police Minister says police can already conduct school checks if they suspect trafficking is taking place

Police Minister says police can already conduct school checks if they suspect trafficking is taking place Police Minister says policy will be poor use of police resources

Police Minister Peter Malinauskas labelled Opposition Leader Steven Marshall's plan "ridiculous" and "absurd".

"Steven Marshall needs to make his mind up — does he want to be the Premier of the state or the Police Commissioner," he said.

"He's attempting to be both and that's an extraordinary proposition and one that I think South Australians should rather be scared of."

If elected to office at the March state election, Mr Marshall has pledged to implement a series of policies aimed at decreasing drug use, including authorising the police dog squad to conduct random drug checks at high schools.

"I will instruct the Police Commissioner to develop protocols for SAPOL to conduct random inspections of schools by the drug squad to search locker rooms and classrooms for illicit drugs that are placing our children at enormous risk," Mr Marshall said.

At a Liberal Party conference in Adelaide on Saturday, Mr Marshall said as a father of two teenagers, he wanted to win the fight on drugs on "all fronts".

"My message to the drug peddlers, those who are seeking to exploit our kids and subject them to a life of addiction, is simple," he said.

"If I become premier in March next year, your days are numbered. The misery that you inflict on our children will be over."

The searches would be compulsory at public schools, while private schools could opt out.

"Why they are discriminating and only looking at public schools … I've got no idea," Mr Malinauskas said.

Police should focus resources on criminals: Malinauskas

Mr Malinauskas said police already had the power to conduct searches at any school in the state where they had reasonable suspicion drug dealing was taking place.

"This is a policy that the Police Commissioner hasn't asked for and principals don't want," he said.

He said the searches would have to be conducted with existing resources.

"He will be instructing the Police Commissioner to take sniffer dogs away from catching known criminals and instead start sniffing around lockers and lunchboxes — it's an absurd policy," Mr Malinauskas said.

Under the Liberal Party's plans, members of outlaw motorcycle gangs will be banned from visiting prisoners and the fine for cannabis possession will increase from $500 to $2,000.

Mr Marshall said the fines for cannabis possession had not changed in more than 30 years and the state coroner recommended an increase in his inquest into the shooting death of teenager Lewis McPherson.