Preheat your oven to 450°F. Cut off the wing tips of the duck with poultry shears or a sharp knife and remove any excess fat from the neck and body cavity. Rinse inside and out and pat dry. Prick the outer layer of fat with a sharp fork or knife. Sprinkle the salt and juniper over the duck, outside and inside the cavity. Put the sprig of sage inside the duck.
Place the duck in a roasting pan and roast breast side up for 45 minutes. Remove from the oven and flip the duck so that back is up. Return to the oven and continue roasting another 45 minutes. REmove and turn it so the breast side is up again. Continue roasting the duck until it is fully cooked and an instant-read thermometer inserted into the thigh registers 165°F, another 35-50 minutes. Allow the duck to rest before carving.
For the sauce: Put rose hips into a small saucepan and add just enough water to cover. Set over medium heat, bring to a simmer and cook until the rise hips are plump and soft. Strain off and discard rose hips, retaining the cooking liquid, and return to the stove.
Add the chopped sage and season with the honey, to taste. Drizzle the sage and rose-hip sauce over the cooked duck and serve.