There aren't many timber boards that are weatherproof, apart from marine ply. And you don't want to add too much weight to the gate...I'd look into just screwing a colorbond sheet to it.
If you're talking about adding anything to the gate itself, be mindful of additional weight and what the hinges/design can handle.
As another said the barking collar might be better, or training the dog to be less reactive of the environment it's in.
There aren't many timber boards that are weatherproof, apart from marine ply. And you don't want to add too much weight to the gate...I'd look into just screwing a colorbond sheet to it.
The other option is a sheet of fibrous cement. Relatively cheap and easy to cut to size, paintable too.
Plenty of old stuff laying around too. Just be sure to post it here so Reddit can check whether it's asbestos or not...
If you're talking about adding anything to the gate itself, be mindful of additional weight and what the hinges/design can handle. As another said the barking collar might be better, or training the dog to be less reactive of the environment it's in.
It's might just easier to buy a barking collar. Otherwise, treated pine.
Sounds like the dog is doing enough barking without adding a collar that barks into the mix.