Well there are several pond choices for keeping sharks or rays.
1.) premade - poly, rubber or pvc ponds- which generally range from 6-10' Diameter
2.) Above ground swimming pools (with fish safe pvc liners)
3.) D.I.Y. ponds
D.I.Y. ponds can range for a simple pond (like a koi pond) to a pond with a viewing window. Simple DIY ponds are basically a solid wooden frame with heavy duty fish safe pond liners. The DIY Ponds with viewing windows are basically home made aquariums, made of wood, fiberglass/epoxy resin, and a glass/acrylic window.
Any pond for a shark needs to have a Protein Skimmer as part of the Filtration System. But the Skimmer should be able to handle at least 2 times the volume of the pond. In addition to a Protein Skimmer, a Shark Filtration system should include a Sand Filter, Refugieum(with macro Algea & mud(or Live sand), and/or a LR Sump.