Have had the single dog unit for almost a year now, but needed a way to control 2 dogs at once, since only the one with the collar on would behave. When you add another collar to the system (up to 3 total) you lose the beep and tick modes, but that's OK since I never used the beep and the tick didn't always get their attention. Now both dogs behave since they know what's coming if they don't. I probably don't need another one for the 3rd dog, since she sees what happens to the other 2 and magically behaves now.Get more detail about Petsafe Sport Dog, Field Trainer (SDR-FS) Add-A-Dog.
