every time i stack two cakes on top of each other i make a dam then fill the inside of that with filling , i then stack it and cover the outside with butter cream however i never get it to look flawless... when its all done and covered with fondant u can see the bump where the two cakes meet. please help .. i am dying for a flawless clean looking cake.. what am i doing wrong.. help..

Make the buttercream for your dam stiffer in consistency and/or make your filling layer a little thinner. Most of the time it is either or, or a combination of the two.

The dreaded bulge. This can happen with cakes only iced in buttercream and especially with heavy fondant cakes... they are settling.

You can firmly press the cake layers together to help remove excess air hoping that it won't settle more later, or...

you can read this thread from leah_s about her "trick" to help cakes settle:
http://cakecentral.com/modules.php?name=Forums&file=viewtopic&t=633571&highlight=trick