I recently adopted a very active pit/boxer mix named Ducky. She is about 40lbs of nonstop energy. I felt that biking would be a great outdoors activity for both of us.
There were two factors I needed to consider. First, Ducky has a decently high prey drive and she does lure coursing (in which the dogs follow a small, fast lure around a course). So basically she loves to chase little critters and I encourage her to do so! That offers a pretty big safety hazard in and of itself. On top of that, Ducky is terrified of strangers and loud mechanical sounds such as buses and large trucks. We're working on training her around her triggers and biking around quiet suburban areas but I knew I wanted to be completely safe in case she panicked.
Since I had two very big concerns about safely biking with Ducky, I knew I needed a safety attachment. I researched all the common ones and found the Bike Tow Leash to have the best reviews. It also seems to be the most expensive one of the market ($150). I bit the bullet and just hoped it was as good as everyone says it is.
The good news is, it's actually better than I anticipated! It's easy to install, you don't need any tools, and the flexible yet sturdy design allowed Ducky to adjust to it very quickly. In almost any position she can put herself in, it always seems to keep her at a safe distance from the bike.
Two experiences that nearly made me want to kiss my bike tow leash:
The first time, a UPS truck pulled directly next to me, I'm assuming to ask me a question. Ducky completely freaked out and had a meltdown. Luckily, the UPS guy saw that she was terrified and moved on but she never came loose from the bike and she did not get injured trying to escape in her panic. I was able to move her away and calm her down. Without the safety attachment, I cringe to think about what could have happened.
The second time, Ducky spotted a squirrel in the road about 300 yards ahead. She wanted that squirrel! Her running toward it actually propelled the bike forward in a straight line (which was actually fun!). But then the squirrel got the deer in the headlights look and stopped in the middle of the road. I had to put the breaks on before we ran over the little guy and now that we were close he started panicking and running back and forth (this was making Ducky nuts!). I first put the brakes on and then rode around him - with almost no difficultly or effort whatsoever.
We've been biking about 30 mins everyday (about 3 miles of jogging for Ducky) and every time I am still shocked at how well it works and how safe it feels!
I ordered mine from Amazon but you can also get one here: http://www.thedogoutdoors.com/dog-bike-leash.html