I talked to a friend, that had heard from another friend, that said they used salt mixed with the dirt on pulling tracks. Supposedly holds moisture better? The dish soap thing, I always figured it was the glycerin that held the dirt together, much like it "holds" bubbles together. Then there is diluted white glue. I've never heard of it being used, but if it holds dirt together like it does scenery material on model railroads, it may be a viable option also. I was thinking of experimenting with it on an old track at a friends place...unless someone out there knows why it wouldn't work that is. Here in central Illinois, the dirt is some of the best in the country for agriculture, but makes a lousy race track.