Kay Ann,
I use Frontline and it has worked very well. I also give Carina Brewer's yeast and garlic tablets all year round. Some vets believe they repel fleas, some don't, in any case they can't do any harm and the are not expensive.
Go to "Puritan's Pride" Website: www.puritan.com, and take a look at their catalog for the tablets. They are having a 3 x 1 sale now until May 1st.
I know how hard it is to get rid of fleas in Florida. Many years ago I went to visit with my brother there and I saw huge ones sitting right on the dog's flea collar.