Oh, what fun for you guys!
The one time I tried Magnum at straight-line racing, he wasn't at all interested in the bunny. He was too busy being distracted by the other dogs, the wind, the smells, the tall grass on the side of the run, everything but the bunny. Although the people at the race said he'd eventually get used to all the other sights/sounds/smells and go after the bunny, it's not a hobby I can make time for at this point. Someday… He's pretty happy wandering/racing around his two-acre enclosure here at home.
Have a great time!