After my boy was neutered he has not stopped trying to breed with my female. I freaked out when I came around the corner and my male and female were connected (she was in heat) and then I remembered he could not do any damage. Its been over two years and he still has the tendency to breed with my female. I will be getting the female spayed soon so won't have that problem in the future. So as far as do they ever stop humping I don't know.
