There are several ways to kill or discourage fleas. Some are synthetic chemicals, some are considered “natural”, and both work with varying degrees. No one method is 100% effective, and you will almost always have to combine several approaches to get the results you want. Some methods are applicable for indoor pets, but useless for indoor/outdoor pets. You need to choose the set of approaches that best addresses your situation.
Keep in mind that there are regional differences among fleas: what works well in one area may not work well in other areas. You should consult a LOCAL vet, vet tech, or dog groomer to see what is known to be effective in your area. If you think you’re getting biased opinions, ask several people and see what they concur on. Don’t rely on the products available at your local store; there are too many that are just distributed nationally.
Finally, you may find that you need to switch your approaches around from year to year. If you use the same product several years in a row, you may find the effectiveness lessened. Additionally, some years are worse than others, depending on the previous winter, and you may need to strike earlier with stronger methods some years and relax a bit more with milder methods another year.