Do this to determine from where your dog keeps acquiring fleas: First thing in the morning, when your dog has been indoors for approximately 12 hours, thoroughly look him over. Fleas avoid bright light so look under the hair of the rump and base of the tail and inside the back legs for fleas and “flea dirt.”
When you are sure there are no fleas or ticks present, take your dog outside for his usual outdoor activities. Check him over every 20 minutes or just before you bring him indoors again. If you see fleas or ticks you now know the location of the source and can avoid that area or use appropriate outdoor pest control measures. Ask a professional exterminator about outdoor eradication measures.
Check your dog thoroughly the very last thing at night and again when you arise in the morning. If fleas are present in the morning more are hiding wherever the dog spent the night!