Actually, I run w/Ruby and ride my bike w/Ruby (on a leash of course) and she has never tried to stop to sniff or change course to chase something. She's great to exercise with and runs great on a leash and loves the exercise as much as I do. She runs about 14mph when I'm on the bike…any slower and she's pulling. She's even taken me up a pretty good hill at 11mph. If I'm running her (or biking her), even if she sees wildlife (deer, dogs, cats), she has never attempted to stop or alter her course for them. She has looked at me, but knows the drill and knows that I'm not stopping and keeps on running.
And even when I only walk her, she doesn't stop all the time, because I don't allow it and she is handsomely rewarded for good behavior. She's allowed to stop in one spot (halfway thru the walk, run or biking) to sniff, pee, poop, they we are off again. Her exercise outings are just that, for exercise. There are other walks throughout the day that she is allowed to investigate her surroundings more.
So as far as exercise--running, walking & biking, I say basenjis are great companions!