I think you can make hide glue if you find something dead on the shore.
1 cup collegen
1 cup water
3 table spoons of salt
heat these ingredients at 170 until thick, allow it to cool, mix in the sand, pour into mold, wait until it sets up, take out of mold, dry unlit hard.
Do not allow mixture to boil or get overcooked, as this will break the proteins in the collegen.
ps. this is very syinky, so do outside if possible.