Also, I know some will disagree, but I find the coin floor very useful. I'll just build a ridiculous killbox on one side and throw a coin floor on another. I'll hand-kill all the orcs on the coin floor to get increased money, then go get the lingering orcs on the other side.
I can't remember many levels that had me running too hectically for more than 2 rounds or so. Heck, even Crunch, the level I had the most trouble with, when I really figured out I could just sit there and wait for most of the back half without doing very much manual killing (little enough that I could sit on the portal.)