Regarding the leopard shark: You can currently find some good threads regarding temporarily having a leopard in an aquarium in the "Aggressive" forum.
Yes, she could probally have a leopard for awhile in most larger home aquariums.
Regarding the Bat Ray:
Probally not the best idea. Their amazing to look at but probally not well suited to residential aquariums. Excluding their venomous stinger, their born at almost a foot in length. The only time I've seen one in captivity in person, it was a baby in a 2000 gallon lagoon. In the wild they're reach a wingspan of 67cm within 5 years, and than keep growing until they reach almost 6' and reportedly upto 200 pounds!!!
They're also very active swimmers and known to jump out of the water and skim above the surface.
Yes, you can't keep a leopard for more than a few years at most. Yes Bat Ray's are common enough that clam growers can trap them as a pest. But they're probally best left to extremely large commercial aquariums and the ocean
Sorry if thats some bad news.
