you could put some neat fairy on the end of your applicator and put that through. Might make the dog think twice in future.
Heard a funny story from a postie once...
He used to carry a welders gauntlet in his bag. When he got a problem dog, he would put the glove on and go through the gate. He would put his gloved ahnd in the dogs mouth and grab its tongue!

He wouldn't pull the dogs tongue, just holds it. Dog freezes. Won't move. He would then pet the dog and speak to it. All the while, holding it's tongue. Then he would let go and put the glove back in his bag. No trouble from the dog. Next time he goes back... ... no trouble from the dog. It wags it's tail and greets him quietly.
Never tried it myself but...

Thought about doing it to a few customers tho
