I’d tried all the old wives tales.
My bonsai are on the ground and the possums have no issues eating them.
The only thing that has worked is building a full enclosure.
It was very cheap. Just used metal T fence stakes, hammered them in and wrapped strong chicken wire around the enclosed perimeter and also over the top. Tied them to the stakes with wire. Staked the bottom with tent pegs so there’s no way in. Problem solved. However it doesn’t keep the grasshoppers out and it’s a little bit annoying if you want to get immediate access.
So I left the top with a ‘flip top’ open section that I just tie with a few points so it takes about 5 minutes to open.
Also, growing material they don’t eat is a plus, and that material stays outside the enclosure. Unfortunately for those with possums, they adore Crepe myrtle, Japanese maples etc. it might be worth growing Banksia and Casuarina. Possums rarely touch these genus.
If they want to eat something, nothing deters them.
We had 2 dogs and tried all the tricks everyone recommended, but at the end of the day, if they can’t physically get to the bonsai, then it will work.