It is likely you have critters like crayfish, ducks, and turtles eating the plants faster than you can establish them. Aeration is unlikely to make a difference, if not make it more difficult to get plants established because it may reduce water clarity for sunlight penetration. This is due to water movement not allowing suspended particles to settle.
Simply put, your predator/prey relationship between plants and critters is unstable. Take out a bunch of predators to get the balance back in check. You need some big bass and whatever else is required to get a handle on the crayfish. Turtles are minor unless you have a ton of them, or you have lilies of which they target. The ducks, not much you can do unless you sit around the pond day after day to discourage them. Once you think you have a handle on them, go into "desirable plant mode" and plant what you want in your pond. Put cages around the plants to keep turtles out. Simple fence cages should work. Once you have a good base of plants started, it should establish itself and be not much more work.
