To get a Z visa and foreign expert card you do need a 4 year degree, in theory. I taught in China and was given an F visa (I do have a degree). At the time I had no idea this was illegal. It turns out the owner of my school had some pretty influential friends in the local government so they basically looked the other way, or didn't care, so the chances of being incarcerated were nill. I guess it just depends on the school. I have heard stories of teachers getting busted for working on an F visa, but I think it's pretty rare but not a chance I would be willing to take.

Someone in an earlier post mentioned something about China becoming saturated with English teachers. You have got to be kidding me! For one thing, there are 1.3 billion people living there, and most of them realize that to advance in their careers they need to learn English. Second, China can be a rough place for foreigners, and during the time I was there people came and went all the time.