There are several natural remedies that can help kill fleas on dogs instantly. Here are some of the most effective ones:

1. Diatomaceous Earth: This is a powder made from the fossilized remains of tiny aquatic organisms called diatoms. It works by dehydrating fleas and their larvae, causing them to die. Sprinkle it on your dogs coat and rub it in, making sure to avoid the eyes and nose. Leave it on for a few hours before brushing it off.

2. Apple Cider Vinegar: Mix six cups of apple cider vinegar, four cups of water, and a pinch of salt. Spray the solution on your dogs coat, avoiding the eyes and wounds. This will help repel fleas and kill them on contact.

3. Lemon Juice: Mix the juice of four lemons with two cups of water and apply it to your dogs coat. Leave it on for a few hours before rinsing it off. This will help kill fleas and make your dogs coat smell fresh.

4. Essential Oils: Some essential oils, such as citronella, eucalyptus, peppermint, tea tree, and rosemary, can naturally repel fleas. Dilute a few drops of your chosen essential oil into 300-400ml of water and spray it directly onto your dogs coat. Make sure to dilute the oils appropriately, as some can be toxic to pets.

5. Regular Baths: Regular baths with a natural shampoo like citrus Castile soap can help kill fleas instantly. Use a flea comb to remove any remaining fleas and their eggs from your dogs coat.

Its important to note that before trying any home remedies, you should consult with your vet to ensure that your pet is healthy and that the remedies are safe to use. Additionally, natural remedies may not be as effective as commercial flea treatments, so its important to be vigilant and consistent in your efforts to keep your dog flea-free.