Have you tried the new Feliway plug-in? I think it is called Feliway Calming Essence.

One of my indoor cats (Chester) became very upset when the ferals I care for suddenly decided that the best place to sleep is on the ledge just outside the sliding glass door. Chester began spraying because of this. So, I put a Feliway plug-in in the socket just inside the sliding glass door. After about a day of it being plugged in, Chester stopped spraying!

I have also heard from others that the plug-in does an excellent job of calming agitated cats and is a great tool to use when introducing a new cat to the household.

Also, one of the best things about the plug-in is that it does not leave a residue, which the spray does.