Have you got a (guard) dog?

[Highlander]

Collies are very territorial,..as are German Shepherd, all mine are also rescue dogs...of course I dont know your dog, but the aggression showed towards your farrier could still be `fear aggression`,..if in doubt bite, or in this case threaten... which is a different thing to defending you when you are attacked and he is safe

Boredom in a dog usually makes a dog a bit more hyper, they tend to get excited more, it often comes out in all things exaggerated,..i.e. tearing around the garden, in what humans often call their mad half hour,.. barking more, and often moaning or whining