Group One wins don't come easily as Ciaron Maher can attest and of his five victories to date, four have been with mares.

One of them Srikandi has been retired while another, Azkadellia, has been banned from racing as stewards in Victoria investigate the ownership bona fides of the of the mare.

Away from the Azkadellia controversy, Maher will focus his attention on Caulfield Cup hopefuls, Jameka and Set Square, winners of the past two VRC Oaks, who head to Saturday's Naturalism Stakes.

Victory in the Group Three race guarantees the winner a start in next month's Caulfield Cup.

Both mares sit high in Caulfield Cup betting with Jameka sharing favouritism at $15 and Set Square on the next line at $17.

Jameka is comfortably in the Caulfield Cup at number 17 in the order of entry with a number of runners above her already declared non-starters while Set Square is borderline, sitting equal 33rd.

"Set Square is down the order a bit so if she was able to get the win and get herself in, that would be ideal," Maher said.

Jameka's fitness levels are where Maher wants them heading into Saturday's Caulfield feature while Set Square is making steady improvement after missing an autumn campaign.

The mares have faced off against each other at their two runs this campaign.

Jameka finished in front of Set Square when fourth first-up in the P B Lawrence Stakes at Caulfield last month while Set Square was first home of the pair when third in the Dato Tan Chin Nam Stakes at Moonee Valley on September 3.

"I thought leading into the Dato around the Valley Jameka might have been a bit sharper, but her race didn't go to plan," Maher said.

"Set Square sat wide and just flowed into the race really nice.

"On that race I think it would be hard to split them on Saturday."

Maher is planning one more start for the pair before the Caulfield Cup and said he may split them.

He said they would be nominated for the JRA Cup at Moonee Valley on September 30 and the Turnbull Stakes at Flemington two days later.

"It wouldn't matter what sort of grade of race it is, it's just nice timing heading towards the Caulfield Cup," Maher said.

Set Square is the outsider of the two runners on Saturday at $11 with Jameka the second elect at $5.50 behind Tom Melbourne who has firmed from $4.20 to $4 in early betting.