If your dog seems obsessed with licking his bum, he could possibly be experiencing something abnormal. For instance, anal gland issues, parasites (both internal and external), bacterial infections, allergies, skin contact with an irritant, or an abnormal growth around his bum might be the culprit. You can temporarily discourage the licking by applying an e-collar (also referred to as a ‘doughnut collar’, ‘Elizabethan collar’, or the ‘cone of shame’), but this isn’t a fix—your dog should definitely be examined by your veterinarian.