I ran today for the first time with my dog in a harness. I've ran with him a few times in the past 6 or 8 weeks, but always just used a lead attached to his collar.
I just used a 'standard' harness that we had for him, it wasn't specifically bought as a running harness, but it made a huge difference. It's just a 'step in' harness that clips together around his back, and as I said, was originally bought to walk him in, so I'm not sure I'd worry about getting any special harness.
For reference, my dog is a collie/ setter cross, so probably about the same size as a dalmatian.
He'd always pulled a lot on the lead when using the collar, but when he was in the harness, he settled slightly infront of me and to my right and for most of the 10km run, the lead was pretty slack. He did get a bit excited when he saw other people out walking, and when he saw another dog, but was easier to control.
I've also been using a homemade lead, that's about 7feet long, but typically hold a loop in my right hand. I think I'll shorten it and attach it to my running belt the next time we're out.
