Citronella Bark Collar – a very humane type of anti-bark collar. This type of collar does not deliver a shock to your dog whenever they bark. Instead, it sprays some citronella oil underneath their snout. Citronella oil is an unpleasant smell for dogs and they really don’t like the smell at all. Since most dogs have a strong sense of smell, the anti-bark collars that use citronella oil are really quite effective in training your dog not to bark so much.