All I can say is look them up, ask your local vets/trainers, then go and visit them and see where exactly your dog will be staying as all too many have tiny pens
What county are you in?? We are in Suffolk and have found a very good one (our dog is going for the first time in June) where the dogs actually get off the lead time in enclosed areas plus walks off site on extending leads.
I was very fussy when choosing the right kennel - rang quite a few. We have a border collie that does not go on the lead much due to where we live - so off lead time in kennels very important to me.