Hi Norm, Jack and all
One thing that I have heard works is flashing fairy lights. You can buy cheap solar powered versions. Avoid sets that are predictable and just flash on and off constantly. You want the sets that will cycle through a series of different flashing patterns. Hang them in the trees that you want to protect and it seems to keep the possums well away.
I was a little late with this recommendation ,I could just imagine Norms tree looking like Christmas in July.
https://www.leafrootfruit.com.au/control-possums-melbourne/ https://www.cannonpestmanagement.com.au/possum-deterrents/Yes I agree Jack you can't trust those pesky varmints ,everybody knows Norm's possums are the cause
of the anti-maskers (coronavirus conspiracy theorists) not wearing masks in Victoria.

Cheers
Max.