Often used in association with skateboarding culture, a Loc Dog is similar to a "local". Your typical loc dog knows all the spots, connects, shops, filmers, in the area. Even if one is quite familiar with an area, you still dont know shit compared to them. Loc Dog is not exclusive to skate culture either as one can use it to describe, for example, someone who knows where all the good bars are.

When you eat dirt for the first time and leave your family to build a shack in the woods