Problem solver
After 5 years of being happy and confident, our younger cat developed a phobia of going outside and started to use a corner of the utility room as an indoor toilet - perhaps after an fight with a neighbour's cat. Deterrent sprays and even the Feliway spray did not alter her behaviour.
After several weeks of clearing up the mess, we installed the Feliway diffuser near her bean-bag bed - within a week or so she was confident and happy to go outside again.