I would go with the sand, preferably the kind you buy in a bag (not found outside) because then it comes in smaller grains that pass much better for 1/35th
Then, by mixing white glue, water, detergent (to break up water bonds and prevent beading) and a little drop of brown paint (unless its a pacific island scene) add putting this all in an old windex spray bottle
I would then lay down a layer of the glue mix, apply your sand, then using the bottle spray over top of the sand. The mixture seeps down and forms a hard shell.
Be sure to use just a thin layer of sand, or else you will end up with non stuck sand above and under your fixed sand.

note on the right side, all the cracked peices under the hedgehog. When i did this, i only put white glue over top, and my sand was too thick so only the top half of the sand was glued, when disturbed, it cracked as you see there.
Finally, after all is done with your base, then place any figures, vehicles, tall grass etc., then lay down one final thin layer of sand and glue
Also, as the glue is halfway done drying, it is easy to make footprints/tracks