I have kennelled Rosie twice, and never again. The second time was for a holiday where my usual dog-sitter (Mum) was with us, so her dog and Rosie went together. Rang the kennel after a couple of days to see how she was, and was greeted with indignation that I would want to "check up on them" - ah, no, I want to check on my dog, actually. Turns out they had reason to be feeling guilty about my "checking up". Rosie had developed separation anxiety, and was refusing both food and water, and was scouring anything that they did manage to get into her. In the 10 days she was there, she lost almost 40% of her body weight. She was delivered to Mum (who doesn't drive), who was handed her on a leash, shaking, scared and skin-and-bones, they walked away with NOTHING to say. Mum was horrified (she came home before us), and immediately rang our vet, who dropped everything and made a house call, took Rosie back with him, and she spent a week on a drip getting better.
I was totally horrified that any "professional" kennels would allow a dog to waste so significantly and not bother to contact our Vet (declared on our contact sheet, and about 2 minutes drive from the kennels) or even consult their own (next door, literally)... and when I "dared" question them after, they said they noticed no marked change in her condition and that we were "overreacting".
I swear, I could have committed very bad things that day.
As a result, no more kennels for Rosie. If we have to be away, she is with Mum and her dog, or we don't go. She is our dependant and can't speak for herself, so her well-being is top priority.
Now, this is a "worst-case" experience... if your pooches have been kennelled OK before at the same place, they will probably be OK, but my advice is to make sure that checking in os OK, and they know that they MUST contact you or your vet if ANYTHING is "hinky".