How can I make my creature change a direction?

I have a creature that is moving randomly, but when it hits a "wall" it changes a direction, but I want to go on some random direction, not to move like a ping-pong ball. Can anyone help me with this? Here's my code.

using UnityEngine;

using System.Collections;

public class Random_moving : MonoBehaviour{

     public Vector3 target;
     public float speed=10f;
     int direction = 1;
         void  Start (){
         target = Random.insideUnitSphere * 5;
         transform.Rotate(target);
     }
         void FixedUpdate() {
         
             rigidbody2D.MovePosition(rigidbody2D.position + ((Vector2)(transform.forward * speed * Time.deltaTime * direction)));

     }
     void OnCollisionEnter2D (Collision2D coll){
                 Debug.Log ("hit.");
     if (coll.gameObject.tag == "maze" || coll.gameObject.tag == "coin"){    
             if (screenPos.x < Screen.width / 2){
                 direction *= -1;    

                 Debug.Log ("change_2.");
         }
     }
 }

}