// Create a plane and dont let it be modificable in the Inspector
// nor in the Sceneview.

function Start() {
    var createdGO : GameObject = GameObject.CreatePrimitive(PrimitiveType.Plane);
    createdGO.hideFlags = HideFlags.NotEditable;
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Start() {
        GameObject createdGO = GameObject.CreatePrimitive(PrimitiveType.Plane);
        createdGO.hideFlags = HideFlags.NotEditable;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Start():
        createdGO as GameObject = GameObject.CreatePrimitive(PrimitiveType.Plane)
        createdGO.hideFlags = HideFlags.NotEditable