...and there will NOT be a second. You guys were right. I took my GSD pup (5months almost) and my 4 yr old lab x to a local dog park. I kept my dogs on a leash the first half hour and then took them off for the last half hour. One little pug/chihuawa mix basically attacked Yogi (puppy) by chasing him, barking, and nipping at him. He didn't even engage with the dog. The owner thought it was funny - I wanted to kick her in the face. It was pretty cool though because my very laid back lab x stuck up for him by stepping in front of him and growling at the little dog. If Yogi was smaller, I would have picked him up.
I just put him back on the leash and asked the lady to please keep her jerk dog on a leash too but she ignored me. I finally ended up just leaving because of it. Ridiculous. Plus I had about eight different people come up and ask me what breeder I got him from, how much he cost, how much he weighs, blah blah blah. BUT I did find out (before the mean dog showed up) that he has a beautiful gait while loping and flat out running. He looks like he floats along the ground. Here's a picture of him in the car on the drive home. Keep in mind this is the dog that never stops going.