Just do one wing it will keep them unbalanced so they can't fly. I have heard people say they clipped both wings and they still fly. There are instructions online that show where to clip.
Many Muscovy have flown away from their homes that is why there are so many feral ones. I started out with Muscovy my first came from the river down below us. I never had to clip his wing because he was happy here with his females and never tried flying once he was settled in. My females, I clip...