For people who train dogs for a living, it’s best to buy a SportDOG Field Trainer 425 from the leader in this field, the SportDOG brand. Its e-collars are the most compact system ever sold. It can be used for training in the field, yard, or for hunting. The trainer can switch the vibration, stimulation, and tone to match the dog’s temperament and skill. Some of its features are: waterproof transmitter and receiver can be expanded to control up to 3 dogs and has a transmitter that weighs only 4 ounces. It’s totally easy to handle. This is an upgrade of the sportdog field trainer 400.