I have 3 beautiful cavaliers, all about a year old. I have been walking them a mile every day for several weeks. It is getting warmer and my larger cavalier seems to take a lot longer to cool off (recover) than the two smaller ones. She has a good heart, but, I am worried that maybe the walk is a little long for her as it gets warmer. I do carry water and give them a shot along the way. Is a mile too long for them to walk?