I saw a device on an internet ad-- called
Pet Gentle. Costs about $40, and uses a 9-volt battery.
It redirects dogs by putting out sounds in the 30K decible range. [dogs hear 67 to 45,000Hz and up]. [Humans hear 64 to 23,000]. The ad gave the example of barking dogs, but also works to redirect aggressive ones. They stated after the dogs learned about the irritating noise [for them] they would often stop after a verbal redirection, or even just seeing the device. It also has a light if they need visual enhancement.
People liked this since was much more humane than a shock collar.
Thought it might help w/ that aggressive neighbor dog.