The next option is that of submersible filters. There are few options with these but I have always used the Duetto submersible or internal filters as they are sometimes called. These filters have parts which you can buy separately to create waterfalls. Some people say that they have experienced them getting dirty quickly but I have not had this experience myself I also enjoy the adjustable flow rate that they have.
Another option is that of the hang-on-the-back power filters. These are just what they say they are. A filter with a motor attached to it so that it will draw water over the filter media and then push back clean water into the aquarium. You can use these for turtle enclosures but you have to be careful to watch that the water level doesn’t drop below the intake tube otherwise you risk burning out the impeller. If you do choose to use the hang-on-the-back power filter I would go with the brand name Aquaclear. Next