Charlie goes to dog park at least once or twice a week. It is a enclosed secured park. Charlie does not jump over fence. He gets too busy socializing with other dogs to even think about the fence to get out. He does not want out, too much fun!
If you are nervous, leash her, check around first before you unleash.
Some big dogs do play rough, agressive dogs need to leave right away(the rules says so, including dogs in heat. You also need to pick up your dog poop, there are mutt mits free in the park(city provided) Water buckets are provided too, there is a hose where you can hose down any mud on them before going back in the car. Oh, no digging in the park! The dogs might trip and hurt themself, even human would.
Other then those rules,(keep an eye on your own dog) they are free to run around unleash, play time. I have trained Charlie to come back with a blow of a whistle. You might need to think of something else, because dogs get carry away, too much fun, they do not want to go home.