Dog terrorizing my house / not potty trained like owner said what do I do?

This happens all the time. So many owners blatantly lie. And other dogs are potty trained, but that only applies to their own home. So they may mark your furniture and pee and poop in your house.

I read in your profile that you both leave home for work and saw you have three dogs of your own. So, there's a lot of possibilities for these behaviors. My hunch is that it likely could be anxiety / stimulus reaction (strange house, unknown dogs, humans gone, etc.) His destruction of the kennel leads me to believe he's not crate trained -- when a dog isn't, as you witnessed, that strategy doesn't work (luckily the dog didn't self inflict an injury in the escape process).

While belly bands, diapers, gates, playpens, and crates are the usual go-to tools, it sounds like this dog would do much, much better if there's any way he could return home and you could feed and walk him there. I'd suggest offering that service at the same rate booked and asking the owner if they'd okay just modifying the service that way. If staying at his home is not a possibility, maybe extend that offer to a neighbor friend, family member's nearby home.

I would contact the owner and mention it. That really sucks he peed all over your couch and you. All I can say is go get some belly diapers asap.

Just because a dog is house trained in their home doesn't mean it is house trained in your home. Incidents like this happen every day to lots of sitters so if you are going to be a successful sitter your home needs to be properly prepared. You should have crates and baby gates to contain the dogs in safe easy to clean up areas, have doggie belly bands on hand and also lots of cleaning supplies. Welcome to the world of pet care