Posted: 08/05/2014 at 08:37
Clearly it is not the pot. If you swapped them over and same thing happened.
I suspect animal ...fox perhaps, a cat?......causing urine damage. It may look untidy but try a mesh surround/screen overnight for few nights.
I had damage by my front door years ago by a cat jumping/sleeping on it overnight. I put a circle of clematis mesh around it for week or so and this was sufficient to break the cat's routine.