How do get a three year old German shephard to mellow out.?

He is very hyper even though he has a four acre fenced in yard to run in. Chains and leashes are for peple who don't care that much for their dogs. He also gets plenty of attention from us and the kids. When you tell him to go he does for about three seconds then he is in the way again. He is so annoying when working in yard or doing some thing that don't involve him.