Following your post I have investigated scenic products and techniques. There is vastly more available than when I did scenic modelling a long time ago. Woodland Scenics' range is enormous and their site gives lots of tips, although there is much scope to save money by scratch building, for example building a rock face using crumpled aluminium foil as a mould (or, I have just thought, use the crumpled aluminium directly as the rock face after strengthening on the back with plaster or squirty foam from DIY shops, then paint the aluminium.)
What about pappadums? You know, the very thin bready things that are cooked to be eaten with curries. Here is one we have just eaten:
25 secs. in a microwave on full power, or turned down a bit in time and/or power if necessary for a less violent crinkly effect.
View attachment 98591
View attachment 98592
You could back it with plaster for strength and paint directly on the surface. I've practised this and the effect is good for churned up mud or, if a less crinkly pappadum is produced, for rocks. Mind you, if you have rats, your scene might look moth-eaten after a time.