glenn P wrote:
Put a short, flat (less than a 1/4) piece of anything with a string tied in
the middle in the hole. Pull on it, and fill with plaster. Good as new,
almost.


That is what I do. You can cut a piece of cardboard slightly smaller
than the hold. Put two small holes in it, just large enough to put a
string through it so you can old the string and the cardboard in place
while filling with plaster or mud. When it dries enough, cut the
string off and finish filling hole.