Using a slack line presentation in a productive way to catch fish with spoons or other lures. I use Little Cleos and Husky Jerks when I am fish this way. The Idea is to know where your lure is and control it yet have no influence on it at the same time. It's one of those things in fishing where you know you did it right when you have the fish on the bank. The trick is knowing when to put tension on the line and knowing when to let it ride. The picture below shows how you would do it in theory on a straight run of water with no fluctuating currents. Which we all know is never really going to happen. So here are the steps to give you a idea what I mean.

1. Cast 90° toward the other side of the river, try to calculate where the fish are and shot for 3x the distance out. so if the fish are hugged up against a rock 10 yards from the bank cast 30.
2. Let it sink, try yo keep you line mend up stream from the lure. This is called drag. When heavy object like a spoon is sinking the line will create drag on the lure pulling it down stream.
3. If has not hung up yet let it sink more. Know it's there but don't control it. you should feel its weight in you rod but there should be slack on you line.
4. This is where you start to hang up. give it a little tension just enough to keep it off the rocks. This is where you make or break. What your searching for is where the river is going to grab up you lure and give it action with out your help. If it happens start letting out line if not your going to snag up.
5. Free spool under control, follow it with you rod tip. keep loose but have control of it. This is where you going to start to pick up fish.
6. You have made you presentation, start thinking about your next cast where it will be and how much tweak there needs to get that lure in front of the fish.
7. Reel it in nice and slow. try something different each time, maybe a tug-reel or a tug-tug-reel-drop. I have had fish come with in five feet of me to take a lure, just when I was about to bring it out of the water.
8. take a couple steps down and cast again, relax and enjoy the fact you are fishing.