Kidney stone issue. Else to worry.

My husband was diagnosed with a 7mm kidney stone during routine check for work as he works on board a ship. He had or still has no symptoms at all. He took up 5 sessions of lithrotripsy and still the size remains same and has not passed the stone. Now when we consult another urologist he says the stone can be outside the kidney and so it's not going. However recent CT scan showed it to be 3*4 mm after a month of potrate mb medicine, skipping and good hydration. He is unable to join work due to this as company feels its a risk to send him on board. Kindly advise what to be done. Why is the stone not moving or breaking after 5 sessions of lithrotripsy and can the stone be outside the kidney.. Or anything else to worry..