I used to go mountain biking with my dog. I just let him run free, he loved it. But one time he ran in front of me. We were both hurting, but not bad. I stopped doing that, and just walked him. BTW, I'm glad to hear that someone actually has waited until they were in a good enough living situation to care for a dog before getting one. I wish certain past room-mates had had the forsight you have.