Keeping your dog on leash in an off leash dog park is dangerous and can result in your dog developing leash aggression and other potentially dangerous behaviors. Please do not do this.
You need to work very hard on recall with your dog before he is allowed in a dog park. If your dog is well trained in recall, when he gets too rambunctious with another dog, you can call him to you, let him rest for a few minutes and redirect him to more appropriate play. This is the way the dog will learn and you will be able to have fun at the dog park. Not by restricting him while he is there or hoping he'll "figure it out."
You dog also has to learn socialization skills from other dogs. How to give and receive warnings so that if they are uncomfortable they can tell another dog (IN THEIR LANGUAGE) that they've had enough and want to be left alone. If your dog is restricted or not socialized well, he won't learn these lessons and will not respond to warnings from other dogs. He may eventually take them as a challenge rather than a warning and become rather non-social and aggressive with other dogs. This is not what you want.
Giving a dog free run at a park or anywhere is not as simple as taking off his leash. The dog MUST be well trained and socialized and know that when he is called, he is to come to you immediately. It takes work and you can't expect a dog to know exactly how to behave as WE want them to in a dog park just because we take them there and let them go at it. It is our responsibility as caretakers to guide the dogs into proper behavior, train them, show them alternate ways of having fun rather than antagonizing dogs who do not want to play, etc., etc. Don't expect your dog to just "come around" without your dedicated and hard work.
Good luck.
