I live in Stockton, California, U.S.A. during the down turn in the U.S.A. I have my earth sci. with an electronics certificate. That is how I discovered Davy Jones's videos on You Tube. It taken a little getting used of his personality. I enjoy his videos a lot and kept me entertained. I cannot afford everything he recommends, but I have two multimeters like his and Rigol 50 MHz. That is my only oscilloscope. I cannot afford a signal generator, so I made one out of bread bread with transistors and two selector switches with a schematic diagram from Delton Horn book, "Test Equipment You Can Build."
We have a backyard neighbor with three large dogs that smells and barks when I am cleaning my mother's yard. I have blocked all the small holes in the cedar fence where the dog places his nose to take a smell of my mother's backyard. The dogs are annoying. Over time, the dogs will get used of me and the barking will be less and the risks of you getting bitten will be less, too. Check make sure the dog does not tunnel into your yard. My neighbors dogs have attempted to tunnel into my mother's back yard. I have in filled the tunnel underpass and place a few surplus bricks along the fence to prevent further dog tunneling. One night, feral cats have given birth to kittens in my mother's back yard. The cats are not ours, wild, stray, and feral from the streets. We do not feed them, they came. Our neighbor across the street used feed them and stopped recently. That gotten the three neighbor's dog so angry that one or all of them smashed the cedar fence to splinters and slay the three kittens and placed the kitten carcass in line at the patio of my neighbor's backyard. I have to replace the broken fence boards. Neighbors dogs could be a chore and takes adjusting, lots of adjusting. I hope you do not have a pit bull aggressive dog in your neighbor's yard. Some parts of the U.S.A. and Stockton have dogs attacked people in the streets and yards. These are rare incidents.
It might have been an adapted stray dog that learned to be sensitive to all low frequency sounds and barks at it when heard. I do not know what to suggests. Will the low frequency ultrasound causes the neighbor's dog to bark more than presently? It is going to be impossible to tell your neighbor to find another dog as it is their right to have any dog they chose. It is costly to make a sound insulating and better fence. I covered one portion of m mother's backyard fence so the dogs will not see or place their snout, nose to the holes in the cedar fence from fallen off wood knots. The dogs will bark, but less.