CHANGE IN MALE GERMAN SHEPARD BEHAVIOR

Question
I have a 13 month old non neutered male german shepard.  I take him to a dog park (since he was 3 months).  Lately he has become more aggressive towards dogs that he has been around.  He likes to chase them and nip at them.  When he catches up he has a growl that is starting to worry me.  If he is playing with a dog and another one may come over, the three in the mix makes him more growly and agressive.  He never has gotten into it until lately..usually he backs off.  I am wondering if it is the non neutering or if he is just becoming a more agressive dog and what I can do about it.  
My vet told me when he was a puppy that he was a nervous dog because when the vet goes to touch him he turns around to snap at him, and that i need to do something about his behavior.

Answer
A young adult intact male dog at the dog park will have a progressively harder and harder time. You may want to consider other socialization options as it seems like he is not enjoying the interaction as much as he may have in the past. Adolescence is a very sensitive time!

The second problem is that he is has handling issues at the vet. You can desensitize him to handling, take him to the vet and have absolutely nothing happen to him, acclimate him to a basket muzzle just in case and yes do it now! It is important that you get these issues under control now before he gets better at them or takes them further. Your gut instinct is telling you something-pay attention! These behaviors will not go away or fix themselves.

Some good books to read (available at www.dogwise.com) Scaredy Dog by Ali Brown and Dog Parks-staying safe by Cheryl Smith.

Good luck!