From what I've read...in the past...the most likely origin would seem to
be from making a kilt..."also called a Belted Plaid and a breacan feile
[pronounced "breck'n failer" with the final "R" dropped]."  But I don't
know if the word "yard" was used in the Scotish language (??)...but it does
take nine yards to make a "great kilt"...

Here's one description:
  In the early years (starting around 1600), the Scotsman got up in the
morning, took his (approximately) 2 yard x 4 1/2 yard (9 square yard)
tartan (which was both his bedroll and clothing), put pleats in it to suit
his girth, put his belt under it and lay on it, on his back. With the
pleats reaching near the middle of his thigh, he took one side of the
tartan and folded it over his middle, then the other side, then brought the
belt around and fastened it at his waist. He then stood up and took all of
the extra material hanging over the top of his belt, threw it over his
shoulder (pinning it there) and (in most cases) fastened his belt around
it. This was called the "whole nine yards" to distinguish it from the
smaller tartan.

see image of how to fold material for a kilt:
http://www.scottishdance.net/highland/MakingKilt.html

There are websites that show actualy photos of how one lies down to wrap
the kilt around them..and over the shoulder (well, once you stand up).

That's my 2 cents.   But I suggest we let the horse die a dignified death
now...  :o)