I also agree with the energy issue. I have a V that just turned 1 year old and had several others before her. She has been run off leash in a tall weed field for 1/2 to 1 hour a day since she was 8 weeks old. In the Summer when it's warm, I'll take her out just before sunrise while it's still dewy and cool. In addition to that, I also run her off my bicycle with a "Walky Dog" attachment. I let her pull me for a mile once or twice a day. She pretty much runs flat out for the first 1/2 mile at 18 MPH and the slows gradually to 14 MPH at the end. I don't pedal at all, and only brake when going around corners. This really takes the edge off of her, and it only takes 4 minutes.
You also mentioned you use a harness. That's a sure way to get pulled around by the dog. I started mine with a standard collar, and eventually used a choker collar, for a week, to get her under control. Since then, I only use a standard collar.