One of the best ways to halt the advance of it is to put in a butterfly, or as some people call them - a dutchman. Here's a blog post showing a gorgeous one. He really doesn't go into how he made one - so I will.
Apply some glue and pound it in place, using a block of wood to pound on. If you hammer directly on top of the butterfly, you might crack it. Cracks are what we're trying to eliminate!
At least they're free!
(Happy Birthday, mom!)