From Tribbles to Toupees.

The 2006 book Boarding the Enterprise: Transporters, Tribbles and the Vulcan Death Grip in Gene Roddenberry's Star Trek, co-edited by "The Trouble with Tribbles" writer David Gerrold contains a small reference to Bill Shatner's toupee use. On page 36, we have:

"Hair was also a pain at times. Bill Shatner, whose hair was thinning, had to resort to a toupee on every show."

We also have the tantalizing line, albeit not specifically related to Shats: "Wigs came off during stunt fights." During all of Captain Kirk's fisticuffs on Star Trek, one wonders if there were any out-takes in which the toupee was violently disconnected from its host. Of course, adding that to a blooper reel would have likely cost an editor his or her job.

You can buy the book here. Read more about Tribbles and toupees here.