We were having that type pf problem with two of ours. WHen I made the plans to bring our latest addition into the house I bought a diffuser from the vet that has the Feliway stuff in it. You just plug it into an outlet and it does its stuff. It seems to me that it is working 'cause we have had no MAJOR issues with the latest addition just some minor hissing/fussing but no straight out attacks....maybe give that a try?