Leave a "congratulations" bag on their doorstep. In this bag you can provide some chew toys.. for mental/physical stimulation. A frozen Kong (with instructions to stuff with pb or cheese and freeze or whatever the 99cent store has) for hours of soothing peace as they quietly lick their frozen treat. Toss in a Dogs 101 book, business card for good dog trainer, a cute blanket and healthy treats, and you'll look like the best neighbors ever! ;)
Talk to them perhaps? Maybe they aren't aware of it, or aware of how much it is traveling. Also, the dog may be learning. If this is a new pet it may take some adjustment time. I suggest speaking with them first.
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