I have not seen your pond, but unless it has low-gradient slopes and a shallow area I'd be afraid they may have trouble climbing out. Box turtles are pitiful swimmers. They are however quite GOOD at climbing fences or rough surfaces in corners. My enclosure uses 4 x 8 landscape timbers (3 boards high) for the walls, so they cant climb, and refrigerator shelves buried underneath so they cant tunnel out. I dont know how they'd act socially with sliders or painteds; never kept em together. Is there enough land area?