Q:

Tips to beat Defense Grid Awakening level "Waste Disposal"?

I'm stuck on the level "Waste disposal".   I'd like some strategies to beat this level.
The previous level (Turnaround) required a lot of build-and-then-tear-down to turn the attackers back and keep them cycling around until you kill them. This "Waste disposal" level seems that it would permit such a tactic, but I have been unable to beat it that way.
I have gotten as far as the 25th and final wave, but with only one Core left.  Pretty pathetic.

A:

This video provides an excellent way of getting a gold badge on this level.  You have the right idea: you want to make them circle around, and one of the best areas to do so is right at the beginning.

