Only something with big teeth will get through it. I use this netting for my cranes and it keeps them in fine.If you use Phantom's netting I don't see any need to double it up with anything else. No bird of prey will get through that. If you add wire to stop other predators from climbing up there and chewing through it, the wire will stop birds of prey if you cover it all. I'm a little confused when you talk about doubling it up.
In a 30 x 30 you will need a support as it will sag.