This is how you can easily build a custom natural     background for any terrarium.

Time - About 3 hours of work and
    1-2 weeks until adding live animals

Difficulty - Easy

Supplies:
    - 1-2 cans of Great Stuff© foam
    - Eco-earth© or bed-a-beast© type bedding - dry
    - Multiple tubes of black silicon & chalk gun
    - Logs and sticks or anything you want to add
    - Plastic planting pots cut in half if you want to add
        places for live plants

Start with a clean tank

Arrange logs, sticks, and plastic pots (cut in half for live plants) in tank until you are satisfied with their position.

Take all objects out and set aside in the position you want them in. Then spread black silicon on the back sides of the cage 2-3 inches from the back to hide and cover the ugly yellow Great Stuff© foam that your about to spray. (not done in pictures)

Spray Great Stuff© foam around the areas that the sticks are touching the tank to adhere them and also spray around the cage to add texture and raised areas for climbing and basking, in this cage I also added a feeding dish spot. Let dry for at least 1-2 days.

Once dry you can carve the foam and shave it down until you're completely happy with the design. Also, cut off any excess silicon with a razor blade from the sides of the tank.

Then you start adding the silicon to the back of the cage starting in the corner, go a little at a time so you can get the Eco-earth type bedding to stick to the silicon before it dries. I like to use a pair of rubber gloves to spread the silicon around with my hands. Eventually just add silicon to every inch of the background followed by completely dry Eco-earth© bedding or anything else you want to decorate the background with and you're finished.

Wait at least a week or until the smell of the silicon is unnoticeable until you add any animals to the tank.

Enjoy and have fun! Get creative