potty training gone wrong

Question
I have an 8 yr old dog that was very good about going to the door when he had to go potty. Rarely did he have accidents.
Then we took in my niece's 12 yr old dog. They let him get away with everything. He's destroyed our sofas and recliner by lifting his leg..he pees and poops wherever he wants to go.. now MY dog is doing the same thing.
I know the methods of potty training dogs like crate training, etc etc
but not THIS
all I can do is confine them to one room when we leave so they only crap in that room
in the middle of the night they go wherever.....

Answer
hello Linda:

One question would be are either dog intact?
If so this could be a Marking Claiming act.

With dogs this age, there are medical conditions to consider, so rule those out first.

However it does sound as if your dog, is reacting to the other dogs marking behaviour.

Ensuring you clean the areas with a proper Ordour and Stain remover with the enzymes in it that break down what a dog can smell, will eliminate the sign it is a potty area.

Adding the use of a spray such as a No-Go Spray will help.

Teaching both dogs to ring a bell when they need to go out can help.

With dogs of this age, I am afraid there is not much to be done other than retraining and Crate Training is the best method.