After seeing all the Starship failures, having something with a membrane keep things in place seems like an obvious solution. Bladder tanks and "balloons" have been discussed here: Why is an inflatable balloon inside a fuel tank not used to prevent fuel from "sloshing around"?
What other novel solutions, apart from pressurization with another gas, or a bladder tank, have been proposed and tried? For example, have rotating tanks, or other designs such as a tank with a compression arm and membrane, or a heavier liquid or something else like floating pebbles or pouches that can provide enough downward pressure, been tried? Or what about some novel tank design with an intricate coral-like structure inside? What are the advantages and disadvantages of some of these designs?