I don't bring my dog to Yellowstone/Grand Teton National Parks, it's just easier without having to care for him too. Has to be on a leash, not welcome on the hiking trails, not permitted in most of the buildings.
Not a lot of fun for the dog, and difficult on the owner. I just kennel mine near home if I'm going with the family.
Yellowstone is great, GTNP is real fine too. It'll be crowded, traffic will be slow, but... I try to get there every year, or at most every couple of years. I think that you can have a great time there, even in mid-summer. Yes, bring the fly rod! Need a special fishing license to fish the waters of the park as I recall, but that's easy to get.
Enjoy!
Guy
