I had this problem for a number of years. I just kept putting power steering fluid in, sometimes with a leak stopper (which never helped). When I finally got time to do it (full-time college student), I had my mechanic up at school replace the power steering line, which is what he thought was leaking. It turned out that the whole pump was bad, so we replaced that too, and I haven't had any issues since. Have your mechanic check and see where he thinks the leak is; it's probably in the line. It's a lot cheaper to replace the line than the pump, but in my case it was necessary to do both.
There is grease all down the drivers side frame because of that faulty pump, literally down to the leaf spring bracket.