A BT, as is true of any terrier, is an instinctive vermin hunter and, as such, cannot be trusted off leash or in an unfenced-in area AT ANY TIME!! A rabbit or squirrel is enough to send him chasing, which may lead to being lost or hit by a car. This trait seems to worsen with age. A fenced-in yard is ideal, although a kennel run will also contain the BT. Tying him out in the yard is not recommended, because it often leads to constant barking, some aggression, and leaves him open to attacks by other dogs or theft. Invisible fencing is another option, but is only as good as the training you give your dog. Many BTs choose to take the shock in their determination to hunt, and don’t return to the yard. An invisible-type fence is best used when you are out in the yard with your dog. If you do not have a fenced-in yard, your dog should ALWAYS be on-leash when outside.