In melbourne (where I live too actually
) oiled pods that aren't enclosed are defectable. I've also heard (im not 100% sure) that NSW and QLD also have this rule.
What I mean by oiled pods, is there are two seperate pods available to you:
One works in a similar fashion to your panel filter (stock setup), and requires no oiling at all. This is known as a 'dry element filter'. They come in either the panel shape that fits in your stock box, or recently have came in the same shape as pods.
The other is slightly different than the dry element,
and is oiled. You can get them in the panel shape as well as the pod shape, but pod obviously being more popular. I'm not too sure why they oil it, I'm guessing it's able to filter the air much better whilst also having a better air-flow rate.
So if you have a dry element pod that isn't enclosed, the police have no reason to defect you. If you have an oiled pod in the same situation however, they are able to slap a yellow sticker on your windshield
. In most cases the difference between the two is noticable. The obvious touch test is one way to find out (provided the pod is regularly re-oiled to maintain its effectiveness, and no, there wont be much point to simply stop oiling it, as thats what basically makes the pod work as good as it does)
BTW thats a good way to shield it Flat6, but you might want to think about making up a lid for it as I'm not sure if you need to have one for it to be legal. I know when the bonnets down it acts as a lid, but say if you get an unfriendly policeman one night he may get picky and still defect you.
) 
