I am still not understanding the problem the dog pees on your lawn. so that is not good? you want the dog to go at the park? well to get your dog to pee in any one place you have to be deligant. if you do not want your dog to pee on the lawn. you cannot give him the option. you would have to do something like crate him immediatly upon returning home avoiding the lawn. (this will work also if he pees in the house, just replace the word"lawn" with "house" in my post.) then remove the dog from the crate and go to the park again avoiding the lawn. ( if it is the house, i bet you asking how can avoid the house. you will have to get creative like keep the crate by the door or carry the dog in your arms to the crate.) once the dog pees in the right spot, praise, treat, repeat.
My dog Lana does the same thing, she only pottys at my house or at the dog park. I personally like it, cause then i dont have to worry about her pooping on walks, and that means no icky bag to carry around.