You could use products as mentioned prior but just know that even those can't always keep off all fleas. If someone if your apartment complex has animals with fleas they may still come back. We use advantage for our pup and he gets it all year round. There have been times I see him come in from outside and he will have a flea or two on him. So even with advantage or others, there is still going to be a risk of them getting fleas, especially if the root of the problem isn't dealt with. Talk to your neighbors, if you know who it is and see if there is something you can do together to get rid of the fleas-I am sure they don't like them either.