@John ********
"...and return right away to get a 30 day visa exemption. That is a 30 day visa upon arrival." -->> NO, that is NOT a 30 day visa upon arrival. You started correct by saying you get a 30 day visa exemption, and then you changed it wrongly by saying it is a visa on arrival.
Also : OP has to be careful not to do more than 2 border bounces by land without visa per calendar year. Because that is the maximum. Should be enough for 6 months a year though.
Also be careful with land border bounces : choose the right crossings or just use a border bounce company to be sure.