Umm, I'm not sure I follow your metaphor.
The saying goes something like "The lawyer that defends himself has a fool for a client."
While I normally would not dream
of disagreeing with Alex on anything related to sailing, I will make an exception on this one. If you know your rope work, I mean really know
your rope work, I see no reason not to fabricate your own jack lines and tethers, any more than I see no reason not to tackle anything else on ones own boat--providing
one knows what they're about.
It could be argued that, in this, as in many other things in life, there's even an advantage to doing it yourself: If
you're knowledgeable, capable and conscientious, nobody is likely to do as good a job on your own stuff as will you.