I do not recommend using commercial mosquito repellent spray on dogs, because they contain toxins that a dog will very likely ingest when it grooms itself.
Generally, dogs should not have much of a problem with mosquitoes because their fur protects them.
But if it is needed, I recommend making your own homemade natural mosquito repellent at home, using any number of essential oils that mosquitoes are known to be avoidant of.
You can dilute eucalyptus oil in water and then spray that directly on your dogs skin. This will give your dog the mosquito protection and needs, and also be safe at same time.
