Rich: There are a number of dog repellents that generally contain several plant oils (mint, castor and others) that either confuse their nasal system enough to make them nervous or are thought to be uncomfortable for them. The record is mixed. But if it is only one dog, there might be a product that is perfect to send that dog off to your neighbors. You would just have to test a few. The products will degrade with fall/winter rains but if you have broken their habit, it might keep them off longer than one might predict. 

Another alternative are the motion activated sprinklers. Cats hate them but my guess on dogs is that they won't work. Deer learn to crawl underneath spray pattern and my guess is that dogs would do the same if they wanted to stay fairly dry. But really, they are generally fine with water. 

Best choice, a fence that they can't jump or dig underneath. Hedges, if they are dense enough will work, if they can't jump over them.  Male dogs will mark their territories on the hedges which can injure some hedge plants but not to the point of death, generally. 

 It would be nice if the owner would fence the dog in. There may be an ordinance about that in your neighborhood but it is kind of a messy tool to use, sometimes. 

I hope this helps. Feel free to call or email me directly if you have more questions. Chip Bubl Oregon State University Extension/Columbia County<personal data hidden> or <personal data hidden>