Hi there! Great question! I'd first recommend treating your lovely border collie with a good quality flea/mite product that you can purchase from your local vet. Then I would wash all his bedding above above 60 degrees, and vacuum all the carpet and lounge areas of your house. If he has allergies to fleas it can take just one flea to set off his allergies! If that doesn't settle it down, you can visit your vet to purchase antihistamines to treat his itch. He could be allergic to the environment or plants in your yard as your vet suggested, in that case the antihistamines with help with that also. I hope that helps!