Great tower defense game. I love the play on words with non-civil engineer. A civil engineer friend of mine once told me that the difference between civil engineering and mechanical engineering is that mechanical engineers make cool weapons and civil engineers make targets *gasp.* Tangent aside, I had a lot of fun playing this game.
Small bug, which I bet you're already aware of, I place two towers if I'm standing perfectly halfway between two points. Honestly though, I always had enough money that accidentally placing a second tower was totally fine.
I'll have to take note of your sound check at the beginning. Very smart way to ensure the player's browser settings are cooperating well with your game.
Great game!