Renewing or getting a new visa in Vietnam?

I'm an American who's been to Vietnam 3 times in the last year, my 1st visa was 1 month single entry, the 2nd visa was another 1 month single entry, and my 3rd visa was a 3 month multiple entry which I have gotten extended for another 3 months.

I got the extension for my current visa in Hue (where I'm currently living), it was done by someone in the government that a friend of mine knew, it came down to the last day left on my visa but thankfully everything worked out. I don't have that option again.

Now my visa is going to expire again in a few weeks and I was looking for help with how I can get another 3 month extension. A friend of mine said to go to Laos for a day and then come back, but when I flew into Vietnam for all my visits, I had to pre-arrange a 'visa on arrival' and show papers proving I had this arrangement before I could board an airplane.

I'm worried if I leave the country they won't let me back in, I teach English part time at a school that doesn't give work visas (so they can't help me) and I very much would like to keep teaching.