Keeping your dog active is crucial to having a healthy pet. All dogs need some sort of activity some more than others and it can be anything from mind stimulation or physical activities. Imagine keeping tarzan locked up in a house all day with know trees to climb or social interaction (bad analogy, I know). It would be a disaster, your house would probably be destroyed and all he would be looking forward too is going outside. That would not be a fair way to treat tarzan nor is it for a dog.
Understand the importance of having an active dog as it is critical for its health.