If he sees them coming in or out of their house, in the garden etc, he strains at the lead and barks like he would like to rip them to shreds. It's very embarrassing. If he smells the other neighbour's gardener while in the back garden he goes mental barking with hackles up, trying as hard as he can to get over there!
He's 8 months old and a large guarding breed (presa canario cross). Apart from when he's being territorial like this he's very friendly to people and dogs, and will greet strangers in the park fine.
How should we address this, or is it just something guarding breeds do?