Clicker training for down

Teaching Keiko to go down on command was the hardest one after conquering the fear of the stairs.  After reading training information from the internet, it talked about getting the dog to first sit, then extend the treat just far enough to require the dog to stretch out his nose.  If the dog moved his rear end off the ground, he heard "oops" telling him he didn't get it right.  If he moved either front paw any distance, he heard the click and got a treat.  This took me about four days of repetition and stretching him further out before he got all the way to the ground.  But once he did it, I stopped and gave him a extra helping of treats and praised him with much excitement...he didn't forget it.  He does down mainly on hand signals rather than voice, so that's the next step, to teach him the voice command along with the hand signal. 

His treats are varied.  He did work with pieces of dog food, but grew tired of it quickly.  His favorite?  Tiny slivers of wieners.  I'm trying other food, because wieners are so greasy.