Just wanted to share in a good, waterproof clay substance i recently came across, It's called Apoxie and is made by Aves. This stuff is 2 part, and when mixed and formed, will cure into a hard, waterproof, non-toxic plastic substance in 24 hours. I used it in my 55 gallon aquarium to create a shoreline slope cross section thing from vinyl-coated wire mesh-with the apoxie laid out on top to provide a more natural looking surface. No bad effects on turtle(except a bit of confusion as to where his old basking went to..lol), fish, or crayfish! Ph seems fine also. Handy for making do-it-yourself things that cannot be purchased! I came across this stuff in a hobby shop--not any kind of aquarium place.