Patrick,
Everything above is sound advice for fishing around the dikes. One good method for fishing the scour holes, is to drift them. This works best with only 1 rod out per boat, but can be done with more. You just have more to tangle them up with. The way we do it down here in Ole Miss is: pull into the hole behind the ****. Look at it, and wherever the most amount of either foam or trash is, ease the boat into that, and try to stop in the foam or trash. Bait your hook, and put enough weight on to get to the bottom, preferably straight down. Hang the bait off of the boat, and release the reel. When you feel the weight hit the bottom, engage the reel. Every couple of seconds, pick the bait off the bottom, and let it back down. You may have to drop some more line; you may have to reel back up. As you're doing this, however, the boat is going to be moving. If you spend long enough there, you may do several big circles in the hole. Try to keep the bait right under the boat. Not possible, really, but try. You're gonna get hung up. You're gonna lose some weights, and some whole rigs. That's just part of fishing the MS river.
Another method we've found productive is fishing the seam around the ****.
Look at where the **** runs into the river (where the rocks end), and there will be a spot where the water is running paralell to the ****, or at an angle to the dike, but flowing into the main flow of water going past the ****. This water is what people mean when they talk about an eddy. There will be a seam or line where the eddy water meets the main flow water. Usually, depending of water depth, there will be a ledge very near this seam. It may be further out than the seam; it may be further in. The best way we've found to anchor is to go straight up into the eddy water a good ways; even if you get to where the water is flowing straight at the ****, it is okay, so long as you have enough rope to reach the boat to casting distance of the seam. Drop anchor, and back directly towards the end of the ****, so as to settle in the eddy water flowing paralell to the ****, or with the flow anyway, and have your stern facing the tip of the dike, or the confluence of the eddy and the seam. Spread your baits along the seam. Often, fish will be lying down in holes in the ledge, just eating whatever comes by. I have learned that, to effectively scatter the bait around the ledge, you need to cast into the main flow, and let it drop from there. If you cast into the eddy water, they'll all end up in the same place.
I'm a new comer to fishing above the *****, and feel that I have enough sense to not anchor somewhere that I'm uncomfortable with, but I am beginning to fish above the ***** some.
For mentoring om seam fishing, send Coach or Bigriver a private message; they have near 'bout perfected it. Coach is the one that showed me how to do it, and has taught me a lot of valuable info with regards to fishing the old Man.
Good luck, and, when you find something that works, please let us know!