Interesting take on it & saves a lot of money in Resin
How do you intend to finish it ? Wooden legs ? Metal frame ?
How deep is the resin Layer ? Using a thinner layer like that not only reduces the amount of resin required but also the type of resin required, normal glasscast would do that I would imagine rather than requiring something like glasscast 50
Tom love that idea as well with the pebbles, although you forgot to machine a couple of fish to set in the resin above the pebbles