Strava

With our dogs we try to make sure they don't exhaust or dehydrate themselves. We take a canine electrolyte solution with us and take regular breaks. When they run full tilt for a while there saliva turns into a white froth, and as they leap over berms, logs, doubles etc this gets streaked all over their bodies. Our rough rule of thumb is if they are foaming at the mouth or struggle to regain breath after a couple of minutes then they need a break.

Allegedly Viszlas are the 2nd fastest breed of dogs

http://theilovedogssite.com/the-5-fastest-dog-breeds/2/

I think a dog doing 40mph would seriously upset strava nobbers.