I use the Pyramid attachment to run my guy (Pyramid Bicycle Dog Leash). I researched both the Springer and WalkyDog attachments, but finally decided on the Pyramid attachment after consulting with my friendly neighborhood science geek. He said that from a Physics standpoint, you want the dog attached low on the bike so that they can't pull you over. My dog is 55 pounds of crazy and even when a squirrel crossed our path, he wasn't able to pull me over. The back tire skipped slightly, but no loss of control. I should mention that if your bike has disc brakes, this attachment probably won't work as it attaches to the bike at the rear wheel.
My only warning about biking with your dog would be to be careful of loose dogs. My experience is that NO dog can resist a crazy dog pulling a bicycle past them.
