My dog ran over another (much smaller dog) at the dog park

I have an 80Lb lab/pitbull mix named Brock. He is the sweetest most gentle dog ever and is very well-behaved around other dogs. I had a couple of accidents happen with him at the dog park recently, though. Brock loves to play fetch. It's all he wants to do, but really the only place I can take him to play fetch is at the dog park. I adopted him a few months ago, so I'm not comfortable taking him to unfenced fields. Normally there's no problem at the dog park, I take him there every single day and he loves to play ball. He doesn't even notice the other dogs, just keeps retrieving the ball and brings it back to me, the other dogs don't play fetch usually so they just do their own thing. The only problem is when he's chasing the ball, he goes into hyper-focus mode and doesn't notice his surroundings. There were 2 separate instances where I threw the ball to an open area (I always wait to throw the ball until there is open space so he won't run into anything) but as he was running after it, another dog ran up to him, directly in his path, and Brock tramples them with no hesitation. I don't think he means to, I genuinely think he doesn't even realize he does it. One time a really small daushsand was running up to him, and Brock jumped in the air to catch the ball and kicked the small dog in the face from it really hard. I felt so bad and the dog cried out really loud, thankfully he was okay, just shaken up. I don't know what to do about this, because I'm doing everything I can to avoid this, but there's not much I can do when another dog decides to run right in front of his path. And when Brock is chasing the ball, there is literally nothing that will stop him and he sprints after it. Is there anything I can do about this? Is it just the reality of dog parks? Also, I should mention, both times this happened the other dogs didn't just happen to get in Bock's way and then he runs them over. What happened was the other dogs would be barking at him and chasing him, trying to play, and purposefully get in front of him, clearly not knowing that Brock is a freight train that won't stop for anything.