Are those home carpet steamers worth it?

I know it won't replace professional cleaning, but I have a formerly abused, senile, incontinent dog and she goes on the carpet every damn day. Should I get the home steam cleaner to have at home or should I just rent a machine every month or so? I rent, so replacing the carpet is not an option. Believe me, I prefer hard floors, but they covered up all the beautiful hard wood floors on this remodel job.