It depends on what kind of tracks the model has. Individual link tracks can be made to sag by using glue with a long enough drying time so you can position them. The one-piece vinyl tracks might glue down, but I usually wind up tying them down with thread or inserting pins in the hull to hold them down. It's easy to overdo this look, too. Treads which sag too much are likely to be thrown if the tank turns. The saggiest tracks have to be the Russian JS2 and JS3.