I have always understood that Dha with the ring guard come from Cambodia or Laos and are usually described as "Khmer". Check here for a comprehensive cover of Dha types. Click on "Sword Index" and on individual pics. Most have a description
http://dharesearch.bowditch.us/
Also attached pics of 3 "guarded" Dha I once owned. They were described as Khmer.
Stu