
I need some help !

I have an aquarium which has gravel as a substrate. I would also like to add sand to the same aquarium. I need a means of dividing the two substrates....I would like some kind of material that would allow me to bend...ie not a hard consistence, as I would like to have a wave type of design....
Also, I am thinking of making it a bit higher ( about half an inch to one inch) than the substrate height, so it wouldn't mix. So whatever I am going to use has to be kind and safe for the fish to touch. Am I making any sense ????!!!






Any ideas, would be very appreciated.
Ana