I would just stand up and move away or just push him off. My dog Mickey humped like a maniac as a puppy (not necessarily us, toys, feather duster, pillows, etc) and we thought that he would stop or at least not be as bad once he was desexed....somehow it didn't change a thing. Hardly a day passes where he doesn't hump something such as a foot if dad is being stupid and lets him - despite me telling him to not allow it - but most commonly his humping blanket...yes, he has a blanket just for humping and if we take that away he humps the rest of his bedding so we figuire best to let him continue with a blanket for only that purpose instead of having him hump whatever he can get his paws on. Not sure if this is common or if it's just my dog but that's a warning that it might not stop after desexing, lol.