I make holsters and have done many lined ones with pig sking and other materials. I glue my lining to the inside of the holster body then stitch the mout and toe of the holster(unles the toe will have a plug. I then burnish the edge of the mouth and toe like I would anything else. I then put glue on the inside edge of the pigskin where the two sides will meet to form the main seam. I then fold the holster and stitch the main seam then bevel the edges and burnish as normal. Since the pig skin is sandwiched between the leather and has been glued and stitched, like Terrymac said it is almost impossible for it to come apart and or fray. If you have done your burnishing correctly the edge should look almost like one solid piece and you should have trouble even seeing the edge of the lining material.