You can build Fort Knox and keep them safe for ever, or you take your chances. I would keep them confined until they can fly. At that point I would let them into the pond. I would feel better knowing that they can fly home. I would also establish a routine which makes them come home each night so you can lock them up. For my ducks it is feeding time. I have very large ducks and they actually get fed 3 times per day. For mallards it may be fine with just twice per day. Mine get food in the morning when I let them out into the secure duck yards. We have lots of coyotees so they cannot go down to the meadow and pond until 10 am. At 10 we let them out and they rush down hill to have water fun. Around 1pm they come home for a small feeding and head back down once done. In the evening they come home to their duck house waiting in front of it to be let in. The food is inside and they want. I open the door, they rush in, and close it up behind them. We have the same routine everyday. They always come home about 30 minutes before it gets dark. My ducks cannot fly. The property is fence with a field fence, but that will not stop a coyote, they simply jump over it. So far we are ok. I do take a chance here, but I tell you my ducks are happy and strong. I would worry less with a flying duck. Anyway, you as the owner has to make a decision eventually. I would not let them free roam until they are 6 months old. They need to grow up first.
