Home Depot, steel mesh 'gutter guard', $1.50 or so for a piece. Stronger than chicken wire, but flexible enough to conform to various shapes.
I can help you do it, it is really easy. I have a grill in my Hood Scoop. I can take a close up pic of mine tonight.
Maddad scoop? Can you post some pics? Mine was already on the scoop when I got it but its just chicken mesh thats bent around the bolts on the bottom of the scoop and JB welded to the top of the scoop.
Honestly, I know it is more expensive, but the APC Mesh stuff you get at Pep Boys, Advanced Auto etc... is a little thicker and stronger than just chicken wire. You can actually use Sylicone Sealant to keep it in place, or possibly just a hot glue gun. The Hot Glue gun would probably work really well. I used Silicone since I don't plan on ever taking it out. It may look gawdy since you can see you splitter, but also, with the stock WRX or STI Fin IC, little rocks get in there and bend the fins in reducing its efficiency, so putting the mesh in to protect it is a good idea.