Presently I don't have a marine tank set up - as I'm still planning for my new Fish Room (currently a storage area). But when I finally get up and running - I plan on have a small shark pond or two (in the 1,000-1,500 gallon range). Although I would love to have a large shark lagoon.
I am still curious as to how someone has a tank of this size in one's home. I went to the Manteo Aquarium in NC that has a few sharks as well as fish and I have absolutely no concept as to how many gallons that specific tank is. The massive size of something like 10,000g + in someone's home (I'm assuming) is mind boggling to me. Amazing, but something I can't wrap my head around how someone would be able to do it.
The shark tanks of NC Aquariums - be it Manteo, Pine Knoll Shores, or Fort Fisher tend to all be in the 250,000 to 350,000 gallon range. With the main sharks being the Nurse, Sand Tiger, and some Sandbars, and Bonnetheads (mostly Fort Fisher).
As for how someone can build a shark tank/lagoon at their home. Trust me - it can be done. I've talked with people who have 20,000-40,000 gallon shark lagoons(often modifed swimming pools) at their home. One guy, I've talked with built a 35,000 gallon inground shark lagoon when he added a large sunroom on to his house. He presently has almost a dozen sharks in it - including 2-3 Blacktip Reefs.