I have never put any out, but I wouldnt put them in spots that are marked fish attractors. Hunt your won spots and mark them on your gps.
Second, I know some people put some kind of "hook" in the top of the quickcrete. That way you can double up a rope and drop them exactly where you want them, then just release one end of the rope and pull it through the hook.
Im sure you will get better opinions, but I think I would drop 2 together. Thats just my opinion of course, othe ways may be better.
You can alos PM Sinkum, I know he has put alot out, still havent talked him into the gps coordinates:D