Yo Vortex!
My Retriever used to run with me (died in March 08) around the streets, always on a lead, always with a poop scoop.
I also used to take him to Rivi as well, off the lead, with poop scoop.
He was a well trained dog who was quite used to the bike but I started along the roads on a lead first then around the fields near my house etc.
In the years he rode with me, i never ran him over either but his nose did get quite close to the front tyre on occasions.
He used to go bananas for the first couple of minutes though so holding the lead with one hand and braking with the other is a skill you will need to develop.
He also wrecked a pile of spokes too with a stick being carried in his gob that he kindly shoved into me wheel.
I never did a proper ride with him in case he slowed me down or got mowed down by me or other bikers and off road stuck to tracks rather than trails.
You will have a pile of fun with the dog if you can train him up. Good luck and let us know how it develops.