Saw a write up on another forum so I decided to post up over here how I made mine. Don't have any videos yet, but this thing produces quite a bit of ripple and bobbing movement in the spread. Great for dead flat days and cheap to make.
-weazle ball (from Crackerbarrel-rip tail part off)
-something to cut the decoy. I used a Dremel tool
-marker to draw where you will be cutting
Cut a whole out of the back of the decoy big enough to easily get the ball in and out.
Next fill the entire decoy up with expandable foam.
Cut out an area to fit the ball in.
Attach the top piece you cut out and you are ready to go. (no pic of the top back on, but my cut was tight enough that I can wedge the top piece back on and it will hold. you may need to figure out some other way by using industrial velcro or something)