@Override
public boolean canBlockStay(World world, int x, int y, int z)
{
    if (world.getTileEntity(x, y, z) instanceof TELeatherRack)
    {
        TELeatherRack te = (TELeatherRack) world.getTileEntity(x, y, z);
        if (te.leatherItem == null) // Leather racks that have no hide should not exist.
        {
            return false;
        }
    }

    return world.getBlock(x, y - 1, z).getMaterial() == Material.wood; // Leather racks without a log underneath should not exist.
}

@Override
public void onNeighborBlockChange(World world, int i, int j, int k, Block par5)
{
    super.onNeighborBlockChange(world, i, j, k, par5);
    if(!canBlockStay(world,i,j,k))
        world.setBlockToAir(i, j, k);
}