Personally, I avoid dog parks at all costs. There are some very nice dogs but there are also people who never showed their dog any kind of manners and it shows. There are also too many people that just unleash their dog and go sit on the benches or stand in the socialize circle and ignore evrything around them. You aren't their to socialize as a person, you're there for your dog to get some exercise and safe play, if you aren't monitoring your dog, that's a problem and when the menaces appear.
I would recommend socializing with friends dogs or with a reputable doggy day care. The one I worked at every dog went through a temperament test before going into group play to gauge what their level of sociability was, if they were not at all keen to dogs, they were 1x1 with the staff only, no dog interaction. If they were good with a small group, say 5 dogs or less, but too stressed in a full group (10-15 dogs) then we'd organize small groups for them. Everyone else that passed was allowed into general group. Our groups were separated by size, big and little with some exceptions (30-40lbs could go either way depending on temperment). And there was always one or more handlers supervising play and correcting any bad behavior (separating play that gets too rough, humping, giving over stimmed dogs a time out in a kennel, etc.)
On a walk, I'd say having a can of corrector spray is useful, or a small airhorn. Corrector spray is just pressurized air, something to break focus and create distance to an unleashed dog coming toward you. Air horn, similar concept but with noise. All you're trying to do is break that dogs focus and buy time for the owner to recall their dog.
