My adopted boy was neutered before he was a year old, I adopted him when he was 2, he was a surrender. I have him a bit over 2 years. NEVER humped anything, what a perfect boy.Christmas Santa bought him a huge teddy bear. Christmas morning when he saw the teddy bear he grabbed it, straddled it and HUMPED it
, I made my un-godly NO noise, he jumped off it and I put it away. NO MORE TEDDY=NO MORE HUMPING. I think it is just a natural instinct in male dogs.