PetSafe, Basic In-Ground Fence, Keeps Your Pet Safely Contained & Secure In Your Yard, Covers Up To 5 Acres With Additional Wire & Flags, Place Flags Around Your Yard & Train Your Pet Where His New Yard Boundaries Are In Fun, Quick Training Sessions Over The Next 2 Weeks, Most Pets Learn Their New Boundaries Quickly, Pet Gets Too Close To The Yard Edge The Waterproof Receiver Collar Reminds Your Pet With A Warning Beep, Followed By A Safe, Gentle Static Correction If He Continues, Add An Unlimited Number Of Pets By Purchasing An Extra Collar For Each Pet.