You couldn't use pre made pools as they could get damadged and that would be as expensive as hell. And to build a proper arena would cost quiet a bit. Couldn't really make a portable one though would be to heavy (even with out the water). I thought about it, but its pretty impractical tbh, would be pretty cool to watch though, but I think the guns would stop being used pretty quick due to the lack of power amphibious robots would be cool and maybe more interesting to watch, but still unfeasible.