How to stop an older dog from humping?

I’ve done an internet search on this topic but none of the results seemed relevant to my situation, so I thought I’d come here . . .

I have an 8-year-old mutt, 65ish lbs, who in the last 6 months or so started regularly humping dogs at the dog park. We don’t have any other dogs at home. He is neutered and has been from at least 6 mos of age.

He has never exhibited this behavior before, and he doesn’t hump people or objects. He definitely likes to engage in dominance displays at the dog park (he gets in a lot of staring contests), and it seems that he singles out unneutered males to hump, although he sometimes humps females as well. Whenever it happens, I tell him to stop and he does within a few seconds. But he will start again at the next visit. It’s really embarrassing and kind of a pain. Any tips on how to get him to stop?

He is otherwise is a very good dog, with no significant behavioral problems.

Can you tell when the behaviour is about to happen? If so, maybe try commanding him to do another behaviour.

Or maybe keep him on a leash and make sure he doesn’t get too close to other dogs.

Take away his credit card?

–Cliffy