I hear that most of the factory trailers have a cable across that area of the trailer to prevent that. Mine came with a non-factory trailer and didn't have this, unfortunately.
Replacing the daggerboard will cost about $1,000 with shipping from BWY. Before I order one, I wanted to make sure I could prevent this from happening again. Hopefully this will encourage any of you that don't have something to prevent this already to do something similar and save yourselves from my misfortune.
I placed two pair of screw eyes into the bottom surface of the trailer bunks where the daggerboard comes down (don't drill/screw through the bunks and into the bottom of the boat by accident!) ran some threaded rod between them with nuts and washers on the ends (I will apply some LocTite to prevent them from coming off), and used a section of 1/2" PVC pipe as a sleeve or roller on that rod.

In the picture above you can see the sad stub of my once proud daggerboard resting on it when it's rope is let down. For any of you that have wanted to see what's inside the daggerboard, here is your chance.
Here is a side view of the finished contraption. I definitely wish I had done this a couple of weeks ago






