Editing Bioactive Vivarium Guide (section)

=== Step 2: Add terrarium mesh ===
[[File:Substrate_barrier.png|alt=|left|frameless|500x500px]]
Cut a piece of window screen mesh or substrate barrier to fit over the drainage layer, give it 2 inches of extra length and width so you can turn the edges up the sides.

This will prevent substrate from slipping around the barrier.

Layer fine mesh over the top of the leca balls, egg crate, or pond filter foam. 

Turn the edges of the mesh upward against the edges of the tank to prevent your substrate mix from falling into the drainage layer.