A big pen that's stocked with some hogs. Sounds like something you could maybe make some money off of during deer season when people lose most of the land they hunt. Just drop them for an hour or so where you know there are hogs and just keep them in the game. But I could see where it could hurt a dog. Being in a pen like that too much, I could see a dog passing up colder tracks in the woods just to look for one hot track
My main use would be to get a good start on young dogs.