I didn't think about him getting dehydrated. I haven't been able to get him to come out from under the deck since this morning. Its a really low deck so I can't even see him. Maybe I will try putting a water dish in the bushes close to the spot that he goes under.
I have an older outdoor male cat that has been very happy and healthy his whole life. We even have a dog that chases him playfully sometimes with no problems. Yesterday he was chased by an aggressive dog that got some of his tail fur.
This dog was only here temporarily(and won't be invited...