Check if cube is in position before placing new cube

Hey I'm trying to build a terrain generator using cubes. I've got a random "hill" segment but when it generates it doubles up some cubes. I attempted to make an if bool type senario to check before placing but it appears to not have worked as well as I hoped.

 for(int hillcount =0; hillcount < 15; hillcount++)
         {
             int randomy = Random.Range(0, maxy);    
             int randomz = Random.Range(0,maxz);
             int maxhilly = randomy + Random.Range (3,10);
             int maxhillz = randomz + Random.Range (3,15);
         
             for(int i2y = randomy; i2y < maxhilly; i2y++)
             {
                 for(int i2z = randomz; i2z < maxhillz; i2z++)
                 {
                     targetpos = new Vector3(0+i2y,0,0+i2z);
                     
                     if(checkIfPosEmpty(targetpos))
                     {
                     GameObject newcube = (GameObject)Instantiate(cube, new Vector3(0+i2y,1,0+i2z), Quaternion.identity);
                     newcube.name = "cube y:" + i2y + " z:" + i2z;        
                         
                 //GameObject newcube = (GameObject)Instantiate(cube, new Vector3(0+i2y,1,0+i2z), Quaternion.identity);
                 //newcube.name = "cube y2:" + i2y + " z2:" + i2z;
                     }
                 }
             }
         }
     }
             public bool checkIfPosEmpty(Vector3 targetPos)
                     {
                     GameObject[] cubes = GameObject.FindGameObjectsWithTag("cube");
                     
                     foreach(GameObject cube in cubes)
                         {
                         if(transform.position == targetPos)
                         return false;
                         }
                         return true;
                 }