I LOVE the breeds you have--have always thought otterhounds were so cool. Mike Brantley showed one for a long time and he was the sweetest dog! We have treated a number of Wolfies and they are also very sweet! Love to see others who travel with the giant breeds

we do canine physical therapy so in addition to treating dogs with orthopedic issues, we condition show, agility and competitive obedience dogs. We use the pool, land treadmill, underwater treadmill and hills.
Like Wicked whippets, we look for school yards, tennis courts, etc. We walk our Mastiffs about 3 miles and they swim everyday but then we have a heated pool for the spoiled kids. If you have a bicycle you can teach your big guys to trot alongside while you ride. that way they are moving more and you are working a bit less. Golf carts are good for that too.
Look for hills to climb with them--going up is good for the rears and going down is good for fronts.
At a show I actually saw someone sitting on the tailgate of their SUV holding the leash of a Doberman while the driver drove really slow. The Dobe trotted behind burning calories and staying fit. Guess there are all sorts of ways to exercise dogs.

Hope this helps. Since we are in Phoenix MAYBE one day we'll be in the same area. Would love to meet your giants.