Here's some more Loch Style wisdom from John Horsey that would also apply to rivermouths and swinging flies, just let it all hang out.
"Whenever you are fishing a sinking line, never, ever, be in too much of a hurry to lift the flies clear of the water to recast. Always bring them up into view one at a time and hang them there for a second or two, before bringing the next one into view. If you spot a fish following one of your flies, stop and let it take it. If it moves back down into the depths always assume it is looking at one of your other flies. Sometimes, they follow your point fly and turn away at the surface with a splash - at this point do not complain to your boat partner, but drop your flies straight back to where it turned away. You will be amazed how many times they come back and take the fly as it lands on the water and begins to sink - another bonus fish!
If you don't have these, then whip on some tying thread and give it a few coats of superglue. Tie them on at distances of 10, 20 and 30 feet from the end of your fly line."