How to keep the car windows clean in the winter?

I have a 1999 Toyota Camry and I am having quite a bit of trouble keeping the windows clean now. I tried the defrosting and defogging methods to clean the windows clean, but nothing seems to work. The windows (especially the back and side windows) are foggy all the time and it's hard to see through those windows while driving. Is there any way to keep those windows clean? Is there any type of car device/ machinery in the car that I can change to keep the windows clean?