DEAR DR. FOX: In a recent column, you mentioned a safe flea control for cats. Rub the liquid between the cat’s shoulder blades, on the back of the neck and behind the ears. The only problem is that our youngest cat, Phoebe, keeps defecating and urinating outside of the litter box. Some cat-rehoming experts tell me that some house-soiling cats never fully recover and use the litter box. He will probably join the remaining 15% as permanent residents for behavioral reasons: being fearful or aggressive toward people, or spraying and not using the litter box.