We don't go to festivals if we can't take our dog. She gets a couple of long walks (although not the 5-6 miles she would get at home) and then chills in the motorhome while we go to concerts etc. We did take her to a concert once but she wanted to sing along so we took her out again!
We expect to have to keep her under control on the campsite and we always pick up after her.
Quite a few festivals have missed out on our custom but by now we know where we are welcome.