https://docs.google.com/file/d/0B9fPcCtD-OFEOEx3N01OYlVvaEU/edit?usp=sharing
This is my current mob farm wich i'm trying to improve. So if you'll try spiders, you'll soon see they don't fall down like other mobs, sometimes they get stuck at top, so i can't control my turtles with time...