It just takes practice!
A new environment is always gonna be exciting and they're not going to want to listen to you. It's something they learn I think.
With Jackson, EVERY single time he came into the house, he got a treat. It was just something he expected (and still does!) Over at my dad's house, they have a huge fenced in yard too and whenever I say "Jackson!" (sometimes I have to throw in the word "treat") he will come RUNNING... even while the other 2 dogs stay and keep barking. He knows he will always a treat. Even when he ran away once, I never scolded him when he came back to me, I still gave him a treat. I wanted coming to me to be a positive thing.
He's not 100% consistent and I really don't trust him off leash, although he has been offleash a lot in my step-dad's yard which is 3 acres with 90 acres of farmland behind us. But not in a while he hasn't. I don't trust the stinker enough yet lol.
As for the dog park... as long as it's fenced in, I wouldn't worry *too* much about it at first. When I first brought Jackson to a dog park, I let him be there for 2 hours and he was sooo tired that he could've cared less about me putting the leash on him. There's been the occasional time that he runs from me but all I have to do is start walking out of the gate and he comes a running. Dog park is a great place to practice because that's where the most distractions are. Just always have treats in your pocket.
I also have a 50 foot training leash I got on ebay and I let him go out and explore the full 50 foot and then say "Jackson, come!" and give him a treat (always something yummy, like chicken jerky, etc). So he's learning. I'm hoping by the time he is 2 years old, he'll be more reliable off leash in an unfenced in area.