I've had my boat scoot back as well. But as I always raise the mast with the boat directly behind the trailer and the mast resting on the rear mast support on the trailer I can simply run a line from the trailer to a bridle hull fitting and it does not move. But I have not done that for a very long time. I think there is now enough friction between the cups under the hull at the bridle and the ground to stop it and I've improved my lifting technique also. (I put more effort in lifting it up than pushing it up.)
Not absolutely sure why but I just don't have that problem any more.

I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!