Airbricks and cavity wall insulation escaping.

We are losing loads of white polystyrene balls via the airbricks. What’s the best way to secure black fibreglass or plastic gauze (like mosquito netting) to the bricks or mortar to prevent this. Cable clips? Sticks- like? Aluminium strip ?We live in a very windy exposed area and the pointing is recessed.

Your air bricks were not sleeved on installation.
Examining air bricks for in-situ sleeves is part of the so called pre-installation survey that cavity wall insulators never seem to do - in fact, most dont do much of anything that their CIGA assn. lists as a necessary check list before installing pumped CWI.

Where you have an air brick open to the cavity, similar to yours, then, before pumping, custom Cavity Brushes should be installed around the air bricks to create a kind of blocking sleeve.
I was told that the same applies where the cavity is open to the neighbour's cavity - there brushes should block the full height of the cavity at the party wall position. I've never seen them do it and dont know how it would be done without opening up the brickwork here & there?

They use a length of chain, drill hole at top and bottom of wall, feed it in at the top and hook it at the bottom and use it to pull the bottle brush through.