That's cheating. It's exploiting a flaw in the game.
Just like in real life, you can't force people to stay somewhere. Having a neighbor leave, even if they are your favorite, is part of the game. Sorry, but I completely disagree with ANY sort of way of forcing a villager to stay in the village. If you don't want them to move, talk to them every day, send them letters, do tasks for them, and IF they do happen to decide to move, you can convince them not to. You go to their house, it'll have boxes. You talk to them, and it gives you the option for them to stay.