How many people is this for?
Here's my idea -
Two square cakes, pvc pipe covered with fondant in between, as the sides. Use medical gauze for the netting on the sides.
Either way, I can't wait to see this one!
Theresa 
Or if you wanted to keep it edible, you could pipe royal icing out to make the netting. It would be fragile, but... Or if you have any Sugarveil icing, you could easily use that! Just pipe it out, pick it up and attach to your cakes like playingwithsugar said.
i love playingwithsugar's idea
i was going to suggest a moon bouncer made of rice krispies and covered in fontant on top of a square double layered cake in a field of grass
whatever you do it will be so cool and i can't wait to see pictures.
have fun
Amy
Thanks everyone for your suggestions. The party isn't until May,so I"ve got an ample amount of time to work it out.
Theresa the cake has to serve about 40 people. The pvc pipe is a good idea.
namaman: I thought about royal for the nets,but I have to a 30min drive to deliver the cake and I'm not sure how it would hold up.
I kind of like the rice krispies idea. That would be the easiest route,I think.
How do you get fondant to stick to the rice krispies? What do you think about taking one those pie lattice cutter and using it on fondant? That would make a great net.
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