There are very distinct positions for each of the dogs. The lead dogs have to have some really special chacteristics because it's generally very hard for a dog to go forward with a whole pack of barking dogs behind them. Most dogs in that situation want to turn around and face the dogs barking behind them. It's also a challenge to find pairs of dogs that are compatible enough to be harnessed at the same position (left and right) and won't fight with each other. The dogs at the back of the harness kind of get thrown around a lot. On turns, they often get pulled sideways and if the sled catches a rut, they also get jerked around so he needs dogs at the back that can handle that.