I run with my 85 pound German Shepherd. He wears an Easy Walk harness (made by the gentle leader people, I believe). The leash clips in front of the dog (on the chest) as opposed to on the back and it's great for dogs who pull and who won't wear a gentle leader. I'd never go hands free with him - he could easily pull me off my feet.

OK, for conditioning, I would assume that your dog is over a year old and in good health, has had recent vet check ups, etc. As Jesvetmed said, don't go out & pound five miles the first day. Be sure to run during the cool part of the day - it's difficult to tell if a dog is becoming overheated & sometimes you won't know until you have an emergency.

Leashes - I use a four foot leash to keep Zack right by my side. I'd never use a flexi because he could easily hit the end of it "full-tilt-boogie" and I'd have to let go. Plus, I don't want to carry that big bulky plastic thing. Finally, a flexi just teaches a dog how to pull on the leash - something I do not need to teach Zack.

I love to run with Zack. I never worry that I'll be hassled. When we get home, he sleeps (yea!). He's 2 1/2 years old & still full of energy. A tired puppy is a good puppy!