Good Morning and welcome. I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
I am so sorry that Pepper is having these issues....it is obviously a territory or jealousy issue with your son that is causing this...
Since you have tried the Feliway already with no success, you will ahve to have your vet rpescribe medication for you. Clomicalm or Fluoxetine are commonly used medications that will decrease Pepper's anxiety about your son or this territory issue and stop this bad behavior.
Take Pepper to your vet for a thorough exam and blood work to be sure this is not a meidcal issue and if this is ruled out, they can prescribe one of tehse medications for Pepper...this has been successful in many of these cases when used along with the Feliway.
Here are other tips:
Try using different types of litter and make sure to clean these areas with an odor eliminator such as Nature’s Miracle.
Use aluminum foil or double sided tape in the problem areas which may discourage using these spots.
This LINK will help with other tips.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please Reply so I can clarify for you
Sincerely, Dr. Loretta