Although Marlan understands and often obeys 'off' in the context of jumping up on people at the dog park, sometimes he feels the need to do it anyways. It is rude and I would like to stop it. And to my dismay, recently took the wind out of an old man!!!
I predict I'll get a lot of "leash him" responses, but if there are any other suggestions, I'd love to hear them!
Baloo was bad for that, leashing him didn't work because he wouldn't do it on-leash.  :whatever:
I basically learned the oh-so-subtle signs that he was *thinking* of doing it and verbally corrected immedietely, with an "EH!!" or "DON'T!!" or, if I had more time, "Baloo OFF!" I got to the point where I could cut him off with his front feet just a teensy bit off the ground, so he kinda bunny hopped and then put all four back down. Some people looked at me funny, but oh well.
He's MUCH better now, but I still make sure I'm close enough when he's greeting people that I can get that correction in if needed.
Baloo - 5 year old black lab
Peanut - 7 year old minpin
Monster - 3-ish year old frenchie/jack, rescue
That is a tricky one because the easiest thing to do would be to keep him on a leash, but you are at an off-leash park so that's not going to work.
I think Kate is right, you just have to try and stop him before he actually jumps all the way up. I bet once you start doing it your timing will get really good and you'll be able to stop him before it happens.
I have the opposite problem, Cooper will almost never do it when off leash, but on leash is still an issue, getting better, but we're still working on it. Good luck.