Looks like armadillo diggin' to me. Game camera would verify. I would say the gasoline in a hole would work, but leftover fuel leaking into the pond could easily kill other unintended critters, fish too.
Do us a favor, if you will, if you catch a 8" crawdad please take a picture with a Ruler behind it. They taste good too but I have only eaten less than 5 or so in my 58 yrs. 100's of pound of 3" to 5" and now my mouth is water'n and no crawdads.
