You can leave the country and come back without a Visa. You will get a fresh 30 days stay. I believe you can fly out and back often but I think if you it by land it's limited to twice a year?
I usually have a 60 day Visa but my return is for 90 days or more. I tell the airline I can get a 30 days extension or even get a retirement Visa once I'm there. Other option is leave the country and come back for another 30 day's or maybe 45 days pending if they still allow 45 days