
are there any bitches in the vicinity.... ?
My boy is now 15m and tends to hump more when the girls are in season or when he gets excited about going out or playing in the garden... when I know he is about to do it I turn my back and push my bum out so he doesnt get to grip me and say no firmly or other times if he is about to jump I put my hand out so that his head touches it and gently knock him back then again a firm no.. he now has got the message although can waiver when the girls are in season which is what we have atm... in your situation its just not acceptable. I find that it is down to timing as you can tell when its about to occur so the firm no is given before the action rather than after.
You could train the down , then if you see him about to hump ..the command can be given at a distance .. he is at a great age to train this command.
While training is in progress you could put a long line on him so that you can grab it before he reaches his intended victim! a firm no and off before he grabs is what works for me.
Is there no way you can pen him in a largish area so he has freedom but not able to reach the guests... whilst his training is being enforced.