I have an 11 year old female cat and a twelve year old male cat who, despite living together most of their lives do not get along. My female cat spends most of her time outside, while the male cat prefers indoors. Both have been neutered and have had issues with crystals in their urine (the male cat recurringly). I have noticed very smelly, dark, crystally urine on some of the furniture- the spraying has even broken a DVD player! Is there any way to stop this behaviour? Any advice would be greatly appreciated!