my bedlington + whippet nibbles her tail all the time, and sometimes other parts, but less often, she has had flea tablets, flea shampoo and front line but still does it, can anyone suggest a reason for this please? she has no sore or bald patches, no little black "bits" that fleas leave behind, she can come and go from the house as she wishes and has plenty of company and a large garden and frequent walks, so don't think its boredom.