Break down the racks of lamb into individual chops. Use a sharp knife to slice between each rib bone to create a single chop. Angle the knife while cutting to follow the same direction as the bones. If you encounter resistance, angle the knife more sharply so that it will slide between the bones. Repeat until all the chops have been separated.
Add the juniper berries to a mortar and pestle. Crush the berries until mostly broken down. Add the chopped fresh rosemary and minced garlic and crush the ingredients together. Add the kosher salt, pepper, and olive oil and blend together. Transfer the mixture to a bowl and whisk in the lemon juice.
Alternatively, you can make the marinade by blending the ingredients together in a blender or small food processor. Pour the marinade over the lamb chops and refrigerate for several hours to marinate.