In my experience (relatively limited), once any predator like a raccoon takes a duck, you need to take that predator out permanently. They aren't stupid, if they got a meal in a certain spot and it was as tasty and defenseless as a duck, they are going to come back every day or two until the meals are all consumed. I've tried tightening up security after a predator attack, and those **** raccoons are smart and persistent once they know there is food on the other side. Had one climb through two strands of very hot wire, and over a 8' tall very tight fence after discovering that the shocks weren't nearly as bad as the food was good.
I'll take my chances on the new ones moving in being naive enough to not brave the fences. I'll only kill the ones that visit my coop after I've lost a duck. I use live traps baited with tuna fish (I wire the tuna fish can right to the trip lever). I hate doing it, but once the raccoon is in the trap, the trap goes into the pond until the problem is solved. A gun would be quicker, but I don't have a firearm big enough to reliably dispatch a raccoon so the water is probably more humane.
