Questions About Making Decorations

[BettaBoysGirl]

I'm wanting to make a specific decoration (designed to hold aquarium plants below, and hold the bamboo, out so it won't rot underwater. I'm wanting to do it out of rocks, and in a triangle box shape. I attempted this with just aquarium silicone glue and rocks... Too flimsy. I've been thinking of using plastic mesh (the stuff for homemade dividers in fish tanks) to make it stiffer but still concerned this might not be stiff enough to support the rocks from bending, any suggestions of maybe a different type of glue, or way to stiffen the structure? Each side will be about 6 inches long, 8 inches tall, will include a roof of rocks, I need some material I can easily cut (making circles in the top to hold bamboo). Making small pots out of rocks and glue are easy, its getting it to stand up without sagging or break that's the hard part.

The interior will need to be hollow, a fish cave of sorts

 

[Peggers]

You can use milliput to hold rocks together, it's what my LFS used to hold the rocks in their marine show tank together.