I exposed my Lab to shooting at an early age. whenever I picked up a gun he was at the door wanting to go. The only problem was that when I was target shooting he tried to retrieve the bullets.
As to a use as a guard dog, he never failed to alert when someone approached the property. If he sensed a threat he changed from a tail wagging friendly dog to a black terror.
In one case someone was attempting to break into the house. His fierce bark stopped the break in cold.