We have three large dogs and the Innotek SD-2000 fence system. The system overall works great, the only downfall is the collars break. We've had four collars fail in 16 months. Something breaks inside of them, they start rattling, and they're gone. Innotek didn't even take the time to pot the electronics in this collars, they're put together so cheaply it's like Innotek didn't care if they broke. Maybe OK if you have small dogs, but if you have big dogs that play hard - you'll be replacing these on a regular basis.............