i don't have a picture available but..
take a piece of 1x4 board, cut it down about 6-8", then take a jig or hand saw and cut out the top and bottom center leaving about 1/2" of wood on each of the 4 sides should be more or less an H when you are done - this is your line spool (I like this over round spools because I can secure the bungie to an end without having to tie anything or use another bungie for storage and I can wrap the line on a post the same way and use the hole thing as a handle rather than having to pull on the line itself - makes it a lot easier to pick up off the ground or boat floor and not have to take my eyes off working birds)
1/8" round nylon utility line; I keep a couple hundred feet on mine but use what you like
1/4" shock cord as the bungee (I use 100% stretch rated cord) - I use about 3 feet; seems to be just about right for play versus pull on the string
6lb down rigger ball (enough weight to hold even a big set but still pull out and pack, and you don't have to worry about water depth or trying to drive a steak into the rocky bottoms of the Columbia)
attach them all inline in that order
I don't tie permanent loops or use clips (so my rig always spools up nice). Make a bight in the line, twist once, reach the loop just made to the main line right about the twist and pull it through - this basically gives you a nice "slip loop" - not a knot! that can go around any decoy keel (with gloves on too) so I don't have dedicated lineless decoys for the string; I can use any in the bag or change when I want - position the face of the loop in different places on the keel to make the each block turn a little differently on pull for more realistic movement