Yes, Brian,
A good guard dog is worth it’s keep.
One of SWMBO’s Labs (a bitch) was not formally trained, but fiercely loyal to her.
As a demonstration when our relationship was getting serious, she suggested I give her a gentle slap on the hand.
I didn’t get a chance to repeat the move. Dora had a firm grip on my hand, without breaking skin, but would NOT let go until ordered.
It wasn’t “Love me, love my dog”, but “If my dog approves, I do.”

We’ve just clocked up 42 years...
We both still miss Dora.