I just ended up buying Sumo a stuffed animal that was about the same size/a lil bigger than him. and its the only thing I let him hump. (its a cow haha) that way if he has the urge he can, but it is controlled to only one thing.
now he is so used to only humping the cow that if I take it away it doesnt hump anything, and I only let him have it once in a while.
I dont know if this will help but it might be something to try ??
p.s.
the way I got him to only hump his cow is everytime hed start to hump something else Id take it away and give him his cow. so he finally gave up and just started humping the cow cause he knew i was going to give it to him anyway.
Good luckk and conrgratulations on your lil boy!!! you will have so so much fun
