There was an aggressive dog at the park a few weeks back when I met with some people from my dog club and it actually pinned one of our dogs down and started growling at her (not my dog a lovely BT named Scarlett) Scarletts Dad pulled the other dog off and I yelled out to the owner (who was sitting on a park bench on the other side of the park) to come and get his dog, he completely ignored me!!! Didn't move a muscle. So everytime his dog came anywhere near ours I yelled and stomped at it to shoo it off I wasn't having it anywhere around us. Owners like that annoy me!
If you have to threaten with reporting to the council if they don't leave them try to get rego details off the dog and DO report them.