Usage of Feliway spray is a clinically tested and proven method on how to stop cats from spraying indoors. There may be other methods too which are supposed to be effective against cats spraying indoors. But, experts say that no method is as effective as the usage of Feliway spray. The spray contains pheromone which calms cats. This Feliway spray method is rivalled by the litter box method. Some people say that the litter box method is more effective than the usage of Feliway spray. But, majority of cat owners in the world prefer Feliway spray. Of course, there is a lot of differences of opinion on this topic simply because this is a highly subjective topic.
Feliway is a synthetic spray which has a psychological impact on cats. This psychological impact is effective in stopping cats from spraying indoors. It has a success rate of over 80% while the litter box method has a success rate of over 60%. Moreover, Feliway is clinically tested and proven while the litter box method is not.
If you ask me to suggest a particular method, I would say try both the methods on how to stop cats from spraying indoors. Cats are tricky animals. You can never know what works with them for sure.