I think you have to have 2 dogs to be classified as guard dogs.
I know as I was bitten by a guard dog years ago I have the scars on my left arm where the b@stud got me!
I got out of the van in a transport yard, walked towards the office, I was half way between the sanctuary of the office and the van and heard a lot of shouting, looked across and saw a effing great alsation coming for me, nothing I could do so it bit me on the arm, (just like they are trained to funnily enough) luckily my watch took most of the bite. Then I 'persuaded' it to let go by continually punching the side of its head, it realsed it was hurting too much and let me go.
I had seen the 'guard dog' sign and seen a sleeping dog in the corner so I thought I was OK. Bloke said crafty thing, he's allways doing that, and laughed it off. Charming eh.
Murky