I would NOT go to the dog park.
You can try working on threshold tolerances with B.A.T. http://functionalrewards.com/BAT-basics.pdf
I've used this with my 2 older dogs, that unfortunately were lacking in thier social graces. Also working one dog at a time is better. I have found even though my girl Kiya can start trouble when she's with the other dogs by herself she is not a problem when it comes to other dogs. My male will not tolerate a strange dog in his face but tolerates them when they don't invade his space.
Lakota - WGSD 1/13/10
Wolfen - WGSD 12/31/14
Bull -WGSD 2-10-10
Apache - Shiloh Shepherd 12/15/02 - 6/9/15
Kiya - Shiloh Shepherd 5/15/04 -12/19/25