Sharks star Valentine Holmes.

Valentine Holmes's grip on Cronulla Sharks No.1 jersey is slipping after all of one game, with Shane Flanagan planning to "share" the fullback role between he and Josh Dugan in Friday night's local derby with St George Illawarra Dragons.

It was a particularly unhappy game at that for Holmes, who was targeted by his junior club North Queensland to the tune of six missed tackles and an NRL-high four try causes in the opening round.

Try-causes are a contentious area, with more than one player able to have a mark put against his name and wingers and centres often copping this despite poor defensive decisions made inside them also contributing to an unflattering tally.

In the case of Holmes's involvement in all four of the Cowboys tries last week however, the call for Dugan's bigger body at the back is clear cut.

While there was little Holmes could do about Justin O'Neill's opening four-pointer, his presence as last line of defence didn't faze Coen Hess or Kyle Feldt in the slightest as they powered through the 90kg Sharks custodian.

There's no guarantee that Dugan's extra 12 kilos would have stopped them either. But it certainly couldn't have hurt, particularly given his reputation as one of the game's better positional and defensive No.1s.

Holmes was also found out of position and beaten to a grubber on Gavin Cooper's match-winning try, an intricacy of the fullback's game that Flanagan admits Holmes is still developing in.

The irony of it all of course is Dugan left the Dragons last year because they wouldn't pay him a "world class" wage.

Now the Sharks are hosing down the fact Holmes was re-signed 12 months ago on fullback dollars.

By these defensive numbers, Flanagan is at least on the money by switching the two.

*21 players registered two try-causes across round one.