Since marking has nothing to do with having to potty, but is territorial, you can only clean up after it, restrict the dog's access, or invest in belly bands. Some owners don't know their dog marks because the dog is rarely taken to other people's homes and dogs have no need to mark in their own homes.
Awhile back, I posted a link to Brandon McMillan's technique to stop dogs from marking, but it essentially consists of tethering the dog very close to where it has marked, The dog will have enough slack to sit or lie down but cannot get away from that area. Then the dog has a timeout of about 20 minutes. Unfortunately, you need to do this immediately afterward. I have tried it a couple of times on one dog who has been staying with me for years, but it isn't enough to train him. For the longest time, the owner was surprised about the behavior but eventually admitted he did it at her parents home. Now, after they've had a baby, the dog is doing it in his own home, so they've begun to crate him.