IMPO - ponds are much better for shark or rays than any normal home aquarium.
More swimming room, & more surface area(O2 exchange) the shark, and can even cooler to look at than a normal large aquarium.
When it comes to shark ponds or any saltwater pond. Filtration doesn't increase at the same rate as pond size - it increases at a slower rate.
Here's what I mean.
Take a 300 gallon shark pond - the filtration rate is roughly the same as a 300 gallon shark tank. At least 5-6 x tank/pond volume per hour or at least 1500-1800 gallons per hr.
Now take a 3000 gallon shark pond. Which may have at least 6x the surface area of a 300 gallon tank. And 10x the volume. Which means to raise the nitrates by 1 ppm in the 3000 gallon tank, then it would take 10 x the amount of waste that it would take to raise the 300 by the same 1 ppm. So generally for ponds around 3000 gallon the filtration system only need to turn over about 3-4 x the pond volume per hr (9,000-12,000 gallons).
If you go to a 30,000 gallon pool (say a inground swimming pool -converted to a shark pool), then your talking about 40-45x the surface area and about 100x the volume of the 300 gallon tank.
The filtration system for a 30,000 gallon tank only need to be about 2-3 x the pools volume per hr(60,000 to 90,000 gallons).
Think I'm wrong - then look at one of the largest sharks tanks in the U.S. - the 6 million gallon tank at the Atlanta Aquarium. It holds 4 half grown Whale Sharks (about 15-20 ft in length), as well as several other 6-12ft sharks. It's filtration system cycles about 4 million gallons per hour(or 2/3 of it's entire volume).