How can I prevent fleas reinfeasting my pup?

[nyc2caligal]

My pup keeps getting reinfeasted with fleas. Unfortunately there r a lot of strays in my neighborhood and even though Dolly is an in house dog, when we go for potty walks and exercise she comes back with fleas. If I had a yard I could spray the yard but no such luxury. I use advantage monthly and per the vet I use the shampoo he prescribed. But every few days we are right back to square one. Thank goodness it is not a major infestation because I only find several but i know for every one there are many, many more. The vets answer was this is 'california and it is a problem' gee thanks doc and that knowledge cost me office visit $. This is a never ending battle, I am constantly flea house cleaning and watching my pup scratch. There has to be a solution. I just posted a question about her scratching and received some excellent and helpful answer. Unfortunately I was unable to include this portion of my question.