Working in fast moving water

[Dewit2it]

(I'm a little unsure of where to post this, so move it if need be)

Have any of you dove in fast moving water?

I have been contacted about doing video for a spey fishing show, and would be having to dive in fast moving streams while shooting video of salmon and trout.  I'm thinking that some heavy ropework will be involved just to keep position. 

I'm figuring that I would need one rope across the river, and on that rope, having a split sheave, and another rope to adjust my position across the stream.  Attached to the first sheave there would be a second, and the line through it would control my position up and downstream.  It would be tied off on one end, and I would be in a ice dive harness on the other. 

Tending may be a problem, as I don't know how well rope signals will work with the extra rigging.

Extra safety ropes across the river will probably be needed downstream, that I could hopefully catch if the main rigging broke.

Any ideas would be would be helpful!

At least I have time to prepare, as I probably won't be doing things like this for a year yet.