My latest fad for terrain making is Gorilla Glue. Note this NOT Gorilla Super Glue, but plain Gorilla Glue. This is the amber thick glue that comes on squeeze bottles, and foams up on setting.
The object here is to take advantage of it's foaming properties.
I read a few years ago here on TMP about putting a few drops in the corner of a model building and pouring gravel on top of it. This was to form rubble. Basically, that is it.
The key is to control the size of the initial bead, which takes some practice.
My first attempt was some U-shaped sangars on stiff board. Unfortunately the bead was too large and so was the gravel. Still useful but I had to make thinner walled ones.
Much more successful were hedgerows. I had some packs of craft plywood plaques that I cut and beveled to look like elongated hexagons. I put a bead along the length and poured fine aquarium gravel on top. This is a great project to end the night with btw. Pour the gravel on and go to bed. Let the foam finish expanding and it entraps the gravel.
The next day dig out the plaques. I usually add a second layer on top of the first. Then, using hot melt glue, jam clump foliage on top of the wall. Paint and flock the plaque to taste. You then have many long geomorphic plaques you can join as the battle setup requires. Add gaps on the middle for … gaps or gates.
I made stone walls in a similar fashion using tongue depressors as the base and cheapest clay cat litter for the stone. (Is it really necessary to say "unused"? 
). These I spray painted with cheap WalMart flat black and then gray. I flocked the edges.
My latest thing is to make river sections from 12" x 4" Masonite plaques. First paint the inner 3" with dark blue craft paint, smearing with green. When dry paint with several coats of Future floor wax. Really, just paint whatever color you think the river should be.
Then, and this is the tricky part , lay down beads of Gorilla Glue, smearing with the nozzle, to make the banks. Spread a little fine gravel on top but really heap on fine sand or model railroad ballast. Paint and flock when dry.
Obviously it does fine on curved sections and intersections.
The key here is to have a large flat surface you are not afraid to stain and at the same time be able to pour back excess gravel or sand. I find 24 or 30 pack beer or soda cartons ideal. (They also make great masking for spray painting…)
You really want to pour the sand , gravel or kitty litter high so the stuff will be entrapped and the set urethane foam adhesive will not show through.
Btw this glue is very strong but due to its expanding not very good for model making. It made a mess when I tried to glue a resin deck to a pirate ship.
worries about not losing his rules stuff.
