There is literally no combination or placement of towers to beat the expert map. I've beaten every map on hard, but no matter what I can't beat the expert map even on easy. I've tried a million different configurations of towers and nothing works.
Man... you should really make your game more complete before uploading it... that's embarrassing. Overall a good concept, but come on, so many things are missing! Sell, upgrade, lives, bosses, descriptions, and more could be added to make this a real game.