I feel your pain. And yes, there are parks that name Dobes as unacceptable. Be sure to read their websites before considering them.
Personally I love dogs, especially large breeds. And I dislike aggressive dogs regardless of size. fwiw, I have been bitten 3 times in my life and it was by ankle biter breeds- all had idiot owners which was actually the real problem. But I digress.
I have always had Akitas and every single one of them loved people. All could have qualified as Therapy Dogs if I had had the time to certify. What we did when we were RVing with them is to tell the campgrounds that they were mixed breed and probably had some huskie or Siberian in them. Most people don't know Akitas well enough to call our bluff and it worked for us every time. I am afraid that this wont work for you tho, as your boy looks like he should and everyone will know he's a Dobe.
Oh, one thing you might consider if you have the time is to certify your boy as a Therapy Dog. A dog that can go to hospitals and nursing homes may convince a dog-o-phobe of the truth.