I used to work at an apartment complex and this can be a huge problem depending on how many units there are and which floor level you live on. If I were you I would contact my neighbors about this and see if they are also having a problem with fleas and if so then you should all treat your apts. simultaneously! Otherwise they will just go back and forth between apts. You need to use foggers in your apts. and leave for about 3 days. When you come back you need to clean your floors before you let your dog back in so it doesnt get toxic by walking on chemical residue. Make SURE you follow the directions carefully on the foggers as they can be VERY dangerous to pets if you dont. Also bath the dog before returning to make sure it doesnt bring any fleas back in. Hope this helps and maybe you should find a natural remedy to use between MONTHLY frontline. I would NEVER use frontline more than once a month on a yorkie!
