I agree. Look for group training classes who only use positive reinforcement. I wouldn't just bring him to a dog park where it's not a controlled environment and he may feel the need to protect/defend himself and feel more vulnerable. A trainer is going to be able to read his body language more, etc. I think a group training class would greatly benefit him.
I found this place, don't know how close it is to you.
Playful Pup | Dog Boarding, Dog Grooming, Dog Training and Doggie Daycare | Waldorf, MD
I have a few places bookmarked, too, but I think they are closer to my house than yours but a few are
The Coventry School Inc. For Dogs and Their People. Grooming, Boarding and Training for your dog. Training By Julie and Associates https://www.sitstayandplay.com/