There's also some overlooked traps almost nobody uses. The Barrel Spawner is a damn powerful weapon once it's fully upgraded and placed in a high place. Barrels that drop from high places explode automatically so you can have a row with your regular traps and, if the wall has space above, Barrel Spawners that keeps spawning and exploding. It's a pretty good trap to add attrition to the waves of orcs.
Also, AutoBallistas are really the only good trap against flyers unless you can place arrow traps on the path the flyers will take.