We have used the Feliway Diffusers for a few years. I have 4 (former) male cats and 2 (former) females (all are fixed ) and I can say that I fully endorse the product. I can tell the difference with our cats when the diffusers are in use vs. when they aren't. It is quite pricey at pet stores and vet offices but

http://www.carealotpets.com/

Is usually a bit less...

good luck!

Trinity