Larry Mullins wrote the book, Bodyguard to the Prophet (CFI, 2010).  CFI seems to always publish those books that are the most provocative for me as an outsider.

Larry guarded President Spencer W. Kimball from killers.

He writes,

Satan had made a serious effort to put to death the president of the Lord’s church through a number of homicidal, vain, blood-thirsty killers.  Yet, even though we have plenty of evidence that these plans were put into play, they were never successful against the Lord’s chosen prophet.  There were a number of other leaders of other fundamentalist churches who lost their lives to these mad men, but the assassins were never able to break through the president’s security.  It is my belief that the security put together during this period of extreme threat was unlike anything the Church has had before or since.  Even now, there is an ongoing security force equal to any imminent menace facing the president of the Church.  He has his own personal security around him every day, and it would be a simple matter to add to it in any way, should the situation require it (p. 25).