I have two of these units. NO COLLARS, but if you already have one of these units, with collars, you can add a second transmitter to extend the coverage area. You can also take a second unit camping or on a trip so you don't have to relocate your permanent unit to travel with your dog. I use two for my yard and take one when I travel to have an instance fence. I love to trade, so I might trade for something of equal value, tools, fishing equipment, boat stuff etc. Price is firm, so please no low ballers. I don't need money, just figure someone could use them to extend their coverage Thanks for looking.