PetSafe YardMax Rechargeable In-Ground Fence (Upgrade to 18 Gauge Wire) Great new invisible dog fence from PetSafe allows you to use up to 30% more of your yard for your dog to roam Choose from standard grade wire or upgrade to professional grade wire upgrades like 16 and even 14 gauge wire Pet Safe YardMax comes with very light, waterproof, reachargeable collar, with charger that can charge two collars at once. YardMax is expandable to unlimited number of dogs (must purchase additional collars)