You will know their sexes in about one month simply by their voices. By 7-8 weeks the girls will loudly quack while the boys sound like they have a sore throat and can't get anything out but a rasping sound. Be aware that you will need to clean the pond quite often. Well it depends on the size, but a kiddie pool will need to be cleaned every 2-4 days so you get an idea. Plus they will eat all the water plants in it. So as cute as a pond sounds, it may not be practical. Most of us use kiddie pools instead. Add a ball valve to the side and you don't have to lift it to empty it. I keep my ducks out of my koi pond at all times. It is actually a very large stock tank, but they will mess it up.