My club uses a system based on a heavy (5 mm?) stainless steel cable. One end is anchored with a really heavy weight . The cable is mounted on a reel, carried on a barge or a floating platform (we often use a section of pontoon). There is a shackle at each position where we want a buoy. As the barge moves down the river we clip the riser cable to the main cable, and buoys to the riser cables with clothes pegs (so that the buoys release if struck). Once we get to the end of the course we put tension on the cable to get a straight line, then drop a second heavy weight.
This works fairly well, but we only use it over a 500 metre course, laying in about 3 to 4 metres water depth. It does depend on heavy anchors, which are scary to handle, so a safe working platform is important. We use as our main weight heavy chain in a large bucket that must weigh about 100 kg. This means when we retrieve we aren't trying to lift all the weight at once, as we can pull in sections of chain, but the weight allows us to put the cable under a fair amount of tension without dragging. Though the placing and tension of the line is what gets the line 90% in the right place, the line can be fine tuned by lifting and repositioning the cable, as it is the cable weight, rather than line tension that is the main factor in keeping it positioned. If a buoy is knocked off its riser we just lift the cable from an adjacent riser and pick up the cable to reattach.
It takes 2 people well under an hour to lay one 500 metre line, although that's after a lot of prep work, checking cables, untangling risers etc. I would think the system would still be viable out to 750 metres - the limit in part being the weight of cable reels - ours is at the limit for 2 people to maneuver. on and off the platform.