peeing inside

Question
I adopted a yellow lab who is 6 years old last March. He has had no problems to speak of except recently, he has started to pee in my basement, near the litter pan.  I am not sure how long he has been doing it because I would see wet spots from time to time, but never suspected him.  About a week ago, my son "caught him in the act"   We have 2 cats, one who is 2. We had him before we had the dog. And we just got a kitten about 4 weeks ago. I'm not sure if that is useful info. or not!  Any suggestions?

Answer
First it would be a good idea to rule out medical problems such as diabetes his thyroid and a number of other problems that can be detected with a blood test-because if a dog pees in the house and never has before,it might be medical

It could also be because he is territorial with the cat-in that case for a while it might be a good idea to block off the basement for a few weeks,or even when you are just out and see if that helps