Fleas can be anywhere anytime. Even in cold weather. In Florida we have up ad down of temperatures. Flea eggs can nest and then flourish. Monthly flea prevention is key! Is it costly, yes. BUT weigh costs of heart worm infestations, deflea baths at the groomers or if ignored, infections from over scratching. Did you know that 1 (one) flea will bite your dog 420x a day?
My personal preference for treatment is Trifexis. It's a 30 day oral tablet. Kills fleas, Mosquitos and heart worms. The tab will start working with in as early as ten minutes ad after 24 hours completely dead.
An IGR, or insect growth regulator is essential if you use topical. Need to destroy larva! And the topical, if used, needs to be applied to the pink if the skin. It goes into the pink fatty tissue ad sweat glands to protect. This is a 30 day activity that can't be forgotten. 1 day off and you could have an outbreak again. And the continuous flea shampoo to kill fleas will only aggravate you more plus make the dog even more uncomfortable.
And keep in mind it doesn't matter if your dog is inside or outside pet. Is all the same bubble!!!!