You can do above ground with concrete blocks or wood with linear inside . get water hyacinth
And some parrot feathers . you can also put a couple koi fish if you like I would also get a pleco for cleaning summer algae. If you make a nice jungle of plants in one part of the pond , you can keep some small fish in there as well so they can hide from the predator fish. And if your arowana does seem to jump a lot in the pond and you're scared it will jump out , you can buy a pond leaf net and cover it . my arowanas never have me the problem of jumping out.
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