After researching Heavy Electro Cannons, AA Rocket Launchers, and Sonic Cannons as high as they will go, along with the Heavy Defense building. Now line the area you want to defend with Laser Walls and place a single Guardian defense structure. First, place two Heavy Electro Cannons down. Then, put two Sonic Cannons on top of these. Next to this, place two Nests each with an AA Rocket Launcher on top. Also, the LC has the best shields in the game so be sure to use them. For added defense, put some artillery in the area. Also be sure to place an SDI when fighting against the ED.