Your strata manager is wrong. Let’s put this another way, if your neighbour was spray-painting his car and paint landed on your car, would it be up to you to erect screens to prevent this.
Or if your neighbour was chucking dog poo into your garden, would you then have to erect a poo-fence? The strata manager sounds like a typical “not my problem” merchant.
Strata is in its infancy in WA and that means you are going to get inexperienced and uneducated strata managers who still have their heads stuck in quarter acre blocks.
Have a look at your by-laws and what is says about interfering with other people’s lots. Then go back to the strata manager and tell him the rest of Australia says he’s wrong.