How do I prevent my Mallards from flying?
1) House them in a pen with a screened roof
2) Have us pinion the ducklings when they hatch. This is a permanent solution as it is a removal of the tip of one wing.
3) Clip the feathers on one wing. This is temporary as the feathers will grow back. But only do one wing as this leaves the bird unbalanced when they try to fly.