I have been working on those nasty tessellated fish for ages and have tried at least a dozen times and messed up.
I think I found the solution.
I entered each row on my checklist software that synchronizes between my desktop and my Palm Pilot. I can check off the check box on each row as I finish it, the rows are numbered so I can make sure I haven't skipped one, and I can reset the check boxes when I'm done.
I FINALLY finished one tonight. Now I am working on a second one to see if I can finish it without having to start over, which means I have a successful solution.