If you decide to get a four-legged personal trainer, aka a dog, you'll need to regularly give your dog a pedicure.
Keep in mind that you may be willing to trim your dog's nails, but your hands may not. Some dog's nails are very hard, so you may be unable to do it yourself. If you can't find someone to help you out, you will have to take your dog to the vet or the groomer for a pedicure. This is an extra cost, which may be a factor in your decision to get a furry friend.
Another option is to use a Dremel tool to file down your dog's nails. However, not all dogs take kindly to the sound and sensation. The Dremel rotates at between 3,000 and 37,000 RPMs (the things you learn from the internet!).