Oskarsmom, desexing will probably have no effect on your dogs humping. It is not sexual.
It's a training thing and OP, you need to step in quickly next time and, loudly, say something on the lines - frogoff and leave Hooch alone. Loud so the other dog's owners hear you. These owners are totally irresponsible and if their dog happens to start doing that to a dog that does not want the attention ,there will be an argument. They need to be told this is innapropriate and they have to control their dog.
I like Seans idea best though. I think that would be really funny.
Border River Pet Resort