Simply do not allow him to do it. A loud "NO" followed by whatever actions you need to do to enforce your command would be perfectly justified here. Stomp your feet at him; move into him so he can't keep his balance and is forced to back up. Knock him over if necessary (not in anger, just enough to make it impossible for him to continue the behavior.)

I mean, think of a female dog (or any dog, really) who does not want to be pestered by a rude dog (and this behavior is rude, even in dog language)--she swings around to face the rude dog, growls, lunges, snaps--if she is firm enough, eventually the rude dog will get the message.

After you have corrected him and made it clear that you are not happy with his behavior AND he has backed off a bit, then you can distract him with a toy, If he won't quit, crate him, not exactly as a punishment, more to enforce your demand that he cannot hump you.

Just be firm--and keep at it. He seems to have established a habit; it may take a lot of consistent corrections (every single time) to make the rule clear to him.

 

I don't know--I've had nothing but males since 1959--I think all of them tried mounting me or people around us--as puppies--on leash because I keep most puppies on leash to stop stuff I don't want them to keep doing (and there are lot of things that puppies do that I don't want repeated)--a quick snap of the leash dismounts a four or five month old puppy and quick "knock that off" to the puppy was enough to stop that in it's tracks. My dogs stay intact all their lives unless a medical issue come up (that would generally be a prostate problem--neutering is generally a specific for things like that.)

I think you could use the same technique on an older dog--I never needed to but...that's what I did.

Good luck.

dobebug