Stocking at a reduced rate and letting them grow and fill the pond is fine, but if a few fish that are not on the management plan get into the pond, they will prosper too, and screw up the management plans. I prefer to stock lots of forage and give it less than a year to populate, then stock with predators. I've seen predators target "different" fish, so I think the "strangers" will be looked at differently than the common forage fish in the pond (that's providing that the predators are large enough to prey on the unwanted species).