Sexual maturity does not equal aggression.
If you want him safe and presentable in public you have to train him, and letting him run loose at a dog park does not equal training.
In fact, things can happen there that would have the opposite effect of what you're trying to do.
Raised hackles and barking could very well mean that he's becoming fearful.
I would suggest you find a trainer who is familiar with the breed.
Last edited by Sunflowers; 12-15-2013 at 03:14 PM.