I am trying to find a treadmill for Murphy to use on rainy days, but I want to make sure that it is long enough. I saw that the dog whisperer says that this is a good substitute for outside exercise, but I can't help but wonder if a full grown golden would be able to fit on one unless it is extra long. I think that Murphy will be about 100lbs. when full grown. (His dad was huge)! So, how long are your goldens at adult age?