Overall, yes, it's OK if the dog has learned how to use it and if it's not overloaded and it fits them comfortably. You should find a backpack suited for your dog’s body type. There are a variety of brands of really great dog equipment out there, and so I would just recommend doing your research and making sure that you follow their guidelines on sizing. If a dog’s backpack is too heavy, they are more susceptible to foot injuries, she said. What you would do first is try to make the appearance of the backpack mean that good things are going to happen, show them the backpack, give them a treat, wiggle it around and ensure that nothing about the backpack's appearance makes them uncomfortable. Next, put the backpack onto the dog while it is empty and with the straps loose, she said. Then, once the dog is comfortable with that, you can fasten the straps. Take it slow, and don't rush the process, so, buy the backpack and get it fitted well before the outing you hope to use it on.