Aside from Spring we are entering flea season. I posted about Seresto collars so don't use them, they are being recalled due to 1,700 dog deaths/seizures. There are other ways to get fleas in a less expensive manner.
1-Buy human grade Diatomaceous Earth. You'll need a large plastic bottle of any kind cleaned and dried. Put a piece of window screen on top with rubber band and it's now a shaker with a top to stop dampness from getting in.
DE works on exoskeletons by wearing then away and anything with a hard shell will be killed.
2-A spray bottle of whatever you can find that you can treat the dog and your fabrics/rugs etc. I use Adams Flea & Tick spray. You can do this every other week but leave it on the rugs for about 5 mins, same for DE.

You can roll the dog onto his/her back and check belly for fleas, that's the easy way. There is also "flea dirt" which is like black hard blood pieces- the fleas excrement so that's ways to tell if you have an issue. Fleas can be born, embedded in your carpet for years before hatching. vacuuming helps a lot.

What works for you? You can get heartworm meds that also treat fleas and other intestinal issues like worms.