I have had no experience with my own pet and a dog park but a few years ago I accompanied a friend and his little mutt to an enormous leash free dog park.
We pulled into a very large parking area and all I could see were all these happy, mongrels running around leash-less. Initially I thought that it was rather nice. My friend opens his car door, the dog jumps out and is off running her little tail off!
She, the sometimes sweet little mutt, couldn't have been happier. This type of dog park offered a wooded type setting that I believe some dogs just thrive in. If I have to guess, I would say that this park is roughly 200 acres of trails, trees, paths and ponds.
My friend and I stayed on the path aside from the occasional running into the woods to "follow the bark." The dog had a meet and greet and butt sniffing session with every other canine in sight. Usually all introductions were pleasant. Aside from the occasional growl, there were no physical incidents at all. Of course this would be totally different if your dog was not socialized and used to being in a setting with other dogs.
My experience with a dog park was actually good however I am still against them. I feel like there are enough risks out there, I have 3 very docile yet very large dogs. I do not want some spazzed out dog coming anywhere near my dogs. I do not think it is safe to assume that every pet owner knows whether or not their pet is the type of pet that would fit in well at a dog park. So Dick and Jane bring ToTo to the dog park. ToTo is a big couch potato at home and loves the neighbors dog, through the fence. Dick and Jane have never put ToTo in a social situation such as this but go ahead and do it without thought. Toto, runs and plays and encounters a slightly more aggressive dog, hackles go up, heads go down, negative posturing noted and a fight in sues. Why? Because Dick and Jane
didn't realize that their couch potato wasn't as social with other dogs as he was with people...or whatever the cause could be.
My point is this. There will always be the chance of a scuffle or fight when you put that many dogs in an area. That is my biggest concern aside from knowing whether or not a dog is vaccinated. Kennel Cough or Parvo anyone? (new beta strain of parvo - attacks older vaccinated dogs) Fleas? Nah...if you use prevention your dog will not get fleas. Moot point. I love the fact that dog parks offer so much to our pets. I hate the fact that there is so much risk involved. I would never take my pets.