Still, we are far enough research and rsource vise it's no longer a problem (there were quite a few close calls before). Our automatic defense system looks like this, going from no-mans-land to the base:
* checkerboard pattern of walls, effectively "dragons teeth" as used on many 20 century fortifications * double concrete wall * laser turrets * a conveyor belt with depleted uranium munition for gun Gateling gun turrets & artillery cannons (each on one side of the belt) * Gatling gun turrets firing depleted uranium munition * flamethrower turrets feeding from the closest oil deposit * piping for the flame turrets & power poles for electricity supply * an artillery cannon feeding from the belt & automatically attacking anything that strays into the no mans land * base stations for construction robots to repair the damage that still occurs, even with such a rather crazy powerful setup
Still, this actually just "holds the line"! Conquering any additional are from the aliens would be still rather hard, with more and more bugs spawning as you try to attach their nests. Well, then we found out Spidertron (a giant spider like robot players can ride) can fire nukes.
The end result is pretty much the ultimate industrialized warefare - a player boards Spidertron stocked with nuclear warhead tipped rockets and proceeds to the are to be cleared, the fires nukes at targets as appropriate. This will clear the nests bug will make many of the survivors very angry - some of them can even take an indirect hit by the shock wave and still charge at you! You can install some close-in laser defense on the Spidertron but it's still a rather dangerous job. The end result - a new area with new juicy resources & space for new factory complexes, totally pockmarked with with burnt out crates from nuclear blasts! These scars apparently never go away (unless you pave them over) you will always see where a nuke has gone off.
Next you place the defenses as described above on the new perimeter (preferably as short as possible, creatively making use of water that can't be crossed). The build new railway lines and build mining outposts connected to those, to feed you smelters and processing plants.
On the place that remains you can place various processing, research, manufacturing complexes, rocket launch silos - or build a computer that runs a game engine. ;-)
Fed by trains bringing resources over endless nuclear scared wasteland and protected by ever vigilant wall of death.