In answer to your original question:
If something is killing your free range birds, then no, you can not free range unless you are happy to lose your birds. That pond is a distance from the house and well screened. From a wildlife perspective, it probably looks to them like it is out in the woods, which is their territory.
I also suspect that whatever is taking the ducks will develop a taste for easy prey and your chickens next to the house will be targeted in the near future.
People with no predators can free range. People who don't mind losing a percentage of their flock can free range. People who have predators and can't stand to have their birds killed must provide protection by means of safe housing.