What to Do about Accidents
All the vigilance and schedules won't always prevent accidents. Accidents happen, even with older dogs. When you catch your rottweiler in the act, you will most likely shriek in dismay, which will startle him. Don't scream. Don't yell. Don't rub his nose in it or hit him. Tell him “No! Out! Out!” and whisk him outside. When he finishes relieving himself outside, praise him.
If you smell urine, but don't know where your dog has gone, you can use a black light. Urine fluoresces under black light. (Nature's Miracle has a black light for pet owners that is available at pet-supply stores.)
What happens when your rottie has an accident and you don't catch him in the act? Can you correct him? Experts disagree on this, but several people have found it is very helpful to show the mess to the dog and tell him that he's been a bad dog. Again, don't yell or scream. Don't hit or rub his nose in it. Your tone of voice should be enough to convince him you're displeased with him.
Once you've corrected your dog and put him outside where he can relieve himself, you need to clean up the mess. Don't use fancy cleaners that are ammonia-based. Most dogs can smell the urine long after those cleaners evaporate. Instead, clean the area with a good enzymatic cleaner made for pet messes, or use plain soap and water and follow it up with white vinegar diluted with water. Vinegar and water help neutralize the smell and make it less likely that your dog will seek to eliminate in that area again. If you don't thoroughly clean up the area, you run the risk that your rottweiler will pick up the traces of odor and use that area when he needs to eliminate again. You may not smell anything, but your dog will.