Dtv - there is no border run. It works like this that you have to leave Thailand for a couple of minutes (even Laos /Malaysia /Singapore /etc). And you come back for next 6 months. But you get not a new visa (like in a border run case). You get a new stamp for 6 months with DTV Signature in your passport. Your dtv visa period remains the same (5 years in total starting from the Original issuance date). You cannot go to immigration office to prolong dtv visa because you to not extend your visa.