https://en.wikipedia.org/wiki/Guard
Bodyguard
"DEVGRU soldiers protecting Hamid Karzai" by http://www.americanspecialops.com/photos/devgru/devgru-bodyguards.php. Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:DEVGRU_soldiers_protecting_Hamid_Karzai.jpg#/media/File:DEVGRU_soldiers_protecting_Hamid_Karzai.jpg
Security guard
"Private factory guard" by Robbie Sproule from Montreal, Canada - Flickr.com - image description page. Licensed under CC BY 2.0 via Commons - https://commons.wikimedia.org/wiki/File:Private_factory_guard.jpg#/media/File:Private_factory_guard.jpg
Prison officer
Border guard
Coast guard
National Guard
Guard dog
"Dobermann". Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Dobermann.jpg#/media/File:Dobermann.jpg
Livestock guardian dog
Guard llama
"Guard llama and flock-enhanced" by Paul Keleher from Mass, US, photoshopped by Zanaq. Licensed under CC BY 2.0 via Commons - https://commons.wikimedia.org/wiki/File:Guard_llama_and_flock-enhanced.jpg#/media/File:Guard_llama_and_flock-enhanced.jpg
Electronic Wachdog
Knightscope
"PnP-Expo-55" by Knightscope Photography Team - http://knightscope.com/gallery/. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:PnP-Expo-55.jpg#/media/File:PnP-Expo-55.jpg