Lab that is getting aggressive with other unaltered males

Question
Hi Kristin,
I have a 4 year old lab that was totally non aggressive when we adopted him at 1.5 years old but has developed some aggression toward unaltered males and doesn't always do as well with aggressive male dogs either.  He has never bitten another dog but we are concerned because he will growl and it's not a playful growl.  
We are wondering how to deal with this behavior.  We still take him to the dog park nearly daily to keep him well socialized but we have to watch him very carefully.  At this point if an unaltered male dog comes up to him he growls and will go toward it if we don't stop him.  He will often still leave the dog and come when we call him depending on how upset he is.
We are also considering getting a second dog.  We had initially thought about adopting a female lab but grew concerned that this might ruin him for the dog park if he felt protective of her.  We are now considering adopting an eight year old lab who is entirely submissive.  Our hope was that this would possibly even improve our current dog's behavior at the dog park if his "brother" was more relaxed around the intact males that he has a problem with.  I should also stress that he is very good with almost all male dogs as long as they aren't overly dominant and he is not an aggressive player at the dog park.  He will often roll on his back to wrestle with a dog and will do almost anything to get other dogs to chase him.  He also tolerates younger intact males better than older ones and we babysat a 10 month old pup who he never acted aggressive toward at all.  

Thank you for your advice,
Mariah

Answer
It sounds like your dog is fine-provided he is in charge. One way to combat this is to continue to take him to the park,but call him over to you,and make him sit next to your for at least 20 seconds. First this will put you in the top spot instead of the dog,and it will also distract him enough for nothing serious to happen and over time he may just come over to you if he feels 'pushed' by other dogs.

It will be ok to adopt another dog for him esp if it a more submissive dog