You will need to enclose the pond somehow. A small wall, maybe 2 ft high, perhaps with a gate, will be sufficient to prevent all but the most determined turtles. A very thick growth of iris, thick plants like that which won’t hamper the look of a pond, don’t die back completely in the cold, could be another option if you are willing to take the time. Include pictures if you can, size of pond, etc. A small garden pond would be easier to enclose, where a big pond would not. You know fish are part of the attraction, find ways to make your pond less attractive to them. If you have favorites of your fish, or high dollar fish, living in the south, I recommend a raised pond. Snakes, possums, turtles, raccoons, have a harder time getting to them. I converted our above ground pool, just a big Intex, into a pond. I love well water! We get seasonal flooding, assorted varmits, large snappers, I saw a beautiful female red rated slider. So a raised pond is best for me here.