PlayerController.cs

using UnityEngine;
using System.Collections;

[System.Serializable]
public class Boundary
{
    public float xMin, xMax, zMin, zMax;


}


public class PlayerController : MonoBehaviour {


public float speed;
public Boundary boundary;
public float tilt;

// Use this for initialization
void FixedUpdate()
{
    float moveHorizontal = Input.GetAxis("Horizontal");
    float moveVertical = Input.GetAxis("Vertical");

    Vector3 movement = new Vector3(moveHorizontal, 0.0f, moveVertical);

    GetComponent<Rigidbody>().velocity = movement * speed;

    GetComponent<Rigidbody>().position = new Vector3(
        Mathf.Clamp(GetComponent<Rigidbody>().position.x,boundary.xMin, boundary.xMax),
        0.0f,
        Mathf.Clamp(GetComponent<Rigidbody>().position.z, boundary.zMin, boundary.zMax));


    GetComponent<Rigidbody>().rotation = Quaternion.Euler(0,0, GetComponent<Rigidbody>().velocity.x * -tilt);
}
}

float moveHorizontal = Input.GetAxis("Horizontal");
float moveVertical = Input.GetAxis("Vertical");

float moveHorizontal = Input.GetAxis("Horizontal");
float moveVertical = Input.GetAxis("Vertical");
Debug.Log("Movement: " + moveHorizontal + ", " + moveVertical); // <-- add this