For avid fans of National Geographic HD, you've now got quite a few more reasons to keep on watching. Aside from upgrading its website with new videos and behind-the-scenes footage, Nat Geo will soon be launching Locked In -- which "provides a look inside a Georgia prison with some of the country's most hardened criminals" -- and Who Knew? with Marshall Brain. Additionally, the popular Dog Whisperer will be making a return, and a number of specials including Herod's Lost Tomb, Secret Service Files, On Board Air Force One and Drain the Ocean are all slated to appear within a year or so from now. Furthermore, it looks as if the network is aiming to "move aggressively into VOD," as it hopes to have the service in 40 million homes over the next year while delivering content in HD to 20 million domiciles.