"I'm having to speak to you far too often fella, the caution is for persistent" the last time I gave on for persistent, I think it was a foul tackle, a couple of very slight dissents then another clumsy challenge that resulted in the card in the 75th.
Assuming they are all 'nothing' fouls, start with a FK, if you give another FK against the same player have a quiet word "That's two now fella, settle it down" , third one a 'public' talking to then fourth one card him.
The closer he gets to a cautionable offence the fewer chances he gets.