Thanks everyone for all your suggestions.
I will be trying out that fire extinguisher method plus carrying a small clamp about 20cm long that just fits in my pockets :-)
I actually went for a walk around the block and guess what. I didn't find the aggressive dog but I did find an elderly labrador walking close to traffic. Deaf as a post.
Anyhow it had a phone number on the collar and its owner was very surprised and bemused to learn she had somehow escaped from the back yard.