If your dog has taken to marking indoors, you will need to take a few steps of prevention and correction to stop the behavior.
If you have not already done so, spaying and neutering your dog may greatly reduce the behavior.
To start, you will need to act as if you are dealing with an 8 week old puppy. Keep your dog in sight at all times, go for frequent potty breaks, and make sure you can quickly intercept your dog if you catch him/her marking. Tell him no and take him outside to eliminate where he is supposed to. I would also advise getting a deodorizing cleaner to clean all the places your dog has marked before. This will reduce the temptation for your dog to remark these places.
I would also enforce a NILIF lifestyle until you have established common ground and communication with your dog. Your dog, just like a puppy, gets very limited freedom that slowly increases as he learns what he can and can't do, and as you begin to trust that he won't mark the minute you turn your back.