Hello and welcome
I have moved your post to this form.
If the pond doesn't have an island- then I would try and lock them up if you can- otherwise Mr Fox will come along eventually
Can you not pen them in the house and attach a run for a few weeks- once they get used to the idea they should be ok- the muskovies and the shell duck especially will not want to be locked up. Is the shell duck pinioned? As it will fly and so will the muskovies if female (the males get too big to get off the ground) you need to get them used to it now before they become adults as then they will never go in. My muskovies fly all over but they are always waiting for me to feed and put them in at night- they are creatures of habit- it will be hard at first and very frustrating but try and persevere - it will be worth it in the end