Get a come-along or Tirfor. Don't know how you name them Down Under but that's a mechanical device that pulls a steel wire rope through itself. It works as long as your stamina allows, under water, completely covered in goo, you name it, only limited by the rope lenght. You just have to clean it afterwards with a high pressure washer and that's it.
Main advantage is it's heaviness and the force it takes. A good size for Jeeps weights 20 kilos+, plus the winch wire. Plus the handle. It takes a lot of time but you can get anything out. Due to its weight you will take EXTREMELY care not to get stuck again, so this will make the small difference between making and breaking. Seriously.
If you don't know what I'm talking about, read here
http://www.landroverclub.net/Club/HT...ry_Tirfor1.htm
This is a site I used to build but stopped as I own no more Land Rover.