Male dog aggression

Question
I have a four year old purebred male beagle.  Yesterday we went to the dog park and he was showing aggression (showing teeth, growling, hair standing up) towards to the other male dogs.  He has lived with female dogs, but when we went to obedience class a few years ago, he had no problems with the other male dogs in his class.  
When we were at the dog park I kept him on his leash and all the other dogs were loose.  
Is there anything I can do to train him not to be aggressive towards male dogs?  Or should we just stop going to the dog park?

Answer
Beagles make great guard dogs. Ours are better at letting us know there is someting afoot than the doberman, rotts, etc. You didn't say what the other dogs were doing (other than being loose, and responsible dog owners should not let their dogs run loose around other dogs. For whatever reason the Beagle was sensing either danger or protecting you or felt there was danger because the other dogs were loose, while the dog class the dogs ae likely all on leash unless you are beyond basic level, but the Beagle likely knows the other dogs in class do not present a threat.

If you have a prong collar you can use it to signal your dog that growling is not necessary, and by telling your dog, its ok, and pet your dog, or immediately engage in some other activity to distract him from thinking about the loose dogs. Good time to engage in some play activity, offer a hot dog, etc. Other than that I would not stop going to the dog park. I would only see this as a problem if he actually tries to attack the other dogs. If you ignore the other dogs your dog should pick up on that and ignore them as well.

Regards,

Henry Ruhwiedel
Westwind Kennels LLC