I use a Don Hume "Border Patrol" style duty holster as a field holster, when using my tractor, anytime security/retaining the holster is important. It is a little heavy, and it cairries the revolver away from the body a bit so it's not a good concealement option.
Shown with my truck/tractor gun, Rock Island M200:
There are a lot better options for field/concealment, a used Bianchi or Safariland is my choice for most applications, something like this thumbreak retention holster I got for my CZ-75:
I find most of my holsters on Ebay.......