We've been going to a local dog park for the last year and nothing bad has happened so far. Apart from one boisterous Boxer thinking that June was a squirrel (his owner got him under control very quickly), we haven't had any problems with other dogs.
I'm sometimes afraid to walk alone, considering that this is South Africa, but I just make sure that I'm there at peak time and not when the park is quiet.
We haven't had any issues with worms, but we did have (and still do
) fleas. We're moving to a new suburb now with a big park two blocks from my flat, so I hope the dogs are well socialized and clean there. I deworm at least every 6 months because of our regularly park trips and the foster puppies that sometimes live here. Revolution is great against fleas and lasts longer than Advantage, but wouldn't it be bad for them to be on it permanently?