Build up your base with heavy defenses. Nod attacks intensify over time and the two Mammoths will be overwhelmed by the superior Avatars quickly. For an effective defense, capture every Avatar you come across by killing it and reactivating the husk with an Engineer. I amassed about 30 then counter-attacked, destroying the Temple defenses in one go! If you need more time, kill the Obelisks at the southernmost entrance, sneak in with a Sniper Team to spot for Juggernauts firing from your base. Once the first Ion Field Distruptor is down, call in an Ion Cannon strike on the two War Factories at the south entrance to buy some time. Against infantry, use a similar tactic on the Hands of Nod at the east entrance. Both entrances have their own Air Towers, too.