Not sure if i understand the question but i guess artillery or be annoying (raider bots) in general.

You lose if they're equally skilled.

Defenses for the most part aren't very metal efficient as opposed to just growing your army and patrolling more land. That said don't be afraid to have some artillery and anti air, these help give you a zone of influence that the enemy can't constantly and freely invade with something stupid like a factory on global patrol spitting out dox or bombers. Just don't overdo it because it can quickly become superfluous and will stall your progression to the point that everyone will ignore you and suddenly you'll be stamped out by an invasion of high tech units or a barrage of nukes.

You can focus on vehicles and increase your factory patrol radius slowly as your army count increases when playing from behind. You can run 12 t1 vehicle factories for a metal income of less than 200 and if you build ants and flame tanks in a proper 5/1 ratio they tend to be metal efficient and can hold you over until the 20 minute mark. Play defensive, use your tanks to defend while you build up at least one t2 factory so you can get t2 economy but you should be trying to expand to support as many t2 factories as possible.

If you don't have much land remember to reclaim. If the enemy is keeping constant pressure to keep you from expanding that means they're constantly leaving metal at your doorstep. With just a few inputs you can create a bot factory that spits out fab bots on a global reclamation and when your economy takes off you can transition them to making healers for your army or lobbers if you need some extra range for attacking something defended by turrets.

From there maybe focus on orbital since it's so often neglected. The orbital titan can help you invade other planets or you could go for massing units from orbital factories that can attack land. Don't forget nukes, they're good for clearing a beachhead on another planet to get a portal up. If you do manage to get a portal down don't be afraid to send fabs through and actually build defenses. I know that contradicts some of what I said but a key tactical structure like a portal should have artillery and anti air to give you a zone of influence on a new planet just like your main base.


When in doubt keep taking new metal nodes and building new factories while you launch constant invasions.