Books on executive protection/bodyguarding (Secret Service style)

[penta]

OK, so. For yet more of the stories I'm writing, I want to do a bit from the perspective not of the principal who's protected, but from the perspective of the bodyguard/executive protection team.

The problem is, I can find nothing on how bodyguarding by the Secret Service, or their equivalents in the UK/Israel/etc, actually works...

Anybody know of any good books, preferably in a Kindle format?