Surely you've been here long enough to know that when a cat suddenly starts peeing outside the box it may be a sign of a UTI. ;)
AKA, Vet visit time. It'll rule out medical VS behavioral issues. Fortunately, UTIs are typically fairly inexpensive to treat... If it's crystals, may take a bit more effort to treat and later prevent a reoccurrence. Crystals are NOT something to play around with, total blockage can result in the premature death of the cat.
I don't know the situation (or Boomer) well enough to say if it's a behavior thing... though I do know that many area rugs that have a rubber (non-skid) backing that can give off an odor that, to a cat, smells like a place to go pee.
After you take him to the vet and determine that everything is okay or get whatever it is treated, I would just pick the rug up. We use a rug as a bath mat, and Kinky loves to go on it when it is damp, as many cats like to do on damp things. We just pick the rug up when we are done with it and throw it over the shower rod. Problem solved.
CatHerder on Jul 20 at 12:57 PM