Randomness in Sudoku solving algorithm

I am using this backtracking soduku solving algorithm which is really good and efficient

    private void solve()
    {
        for (var y = 8; y >= 0; y--)
        {
            for (var x = 8; x >= 0; x--)
            {
                var a = grid[y, x];
                if (a == 0)
                {
                    for (var n = 1; n <= 9; n++)
                    {
                        if (possible(y, x, n))
                        {
                            grid[y, x] = n;
                            solve();
                            grid[y, x] = 0;
                        }
                    }
                    return;
                }
            }
        }
        print();
    }

The thing is i want to add a little change which I haven't been able to do and it is that instead of trying numbers 1 to 9 in order i want it to choose a random number from 1 to 9, and then set it in the grid, without repetition of course.