I was going to write you a book, but Salmo g. just stole my thunder (and was much more efficient in saying what I was going to say). I have a sense that I am more willing to resort to dirty tricks than he is, but even using the filthiest of tactics, I have found little success in moving water much deeper than 6 feet when fly fishing for salmon and steelhead.

"Biter" coho will chase a fly all the way to the surface on occasion, so you don't have to hit them in the mouth. Generally speaking, weighted flies fished off a dry line with an 8-10 foot leader will get you in the game. If they don't, you may do better to move on to the next spot. As for the kings you likely wanted to target in deeper water, keep targeting coho in productive water, and every once in a while, you will hook into something surprisingly heavy. Better to get lucky once in a while than to get thoroughly frustrated trying to do something the vast majority of fly fishers (myself included) can't consistently accomplish.

Good luck!