Working for less than 3 months, is it really ok?

Hi all...been reading that working for less than 3 months means that foreigners are exempt from needing a work visa. I am looking to teach here and know that it's not really as simple as that. Does anyone have experience of this and is it as straight forward as it appears? Would leaving before 3 months and then returning again be classed as a kind of loophole or is that just simply against the law?

Sorry if this has been repeated elsewhere, I did see 1 recent similar thread but not quite the same, hence the new thread.

Thanks!! :)

I believe the less than three month provision is for employees of international corporations on temporary assignment.  Nothing to do with teachers who are generally employees of Vietnamese concerns.

Thanks...I knew it wouldn't be as simple and straight forward as I wanted it to be, ah well wishful thinking...maybe I could create my own company and temporarily assign myself to teach in Vietnam...3 months at a time haha ;)