Unique Randomiser method - C#

Basically i'm creating a method that randomises a number then either returns 0 or the random value. (Depending upon if an array already has that value stored in it). There's currently 2 problems. Not all paths return a value. And the last part of my loop (i++) is unreachable. Any help would be great. Also heres the array that i created for the randomiser:

int[] arr = new int[4];

Heres the method:

public int UniqueRandomiser()        
{
    Random rnd = new Random();

       int j = rnd.Next(1, 4);
        for (int i = 0; i < 4; i++)
        {
            if (rand1[i] == j)
            {
                return 0;
            }
            else
            {
                return j;
            }

        }   
}