Although this product doesn't last as long as it boasts and is expensive, I definately noticed an immediate difference in my cats the same day I started using these.  It stopped them from urine marking completely.  And just as it warns, when you stop using them, your cats start marking again!!  Mine started back up within a week!  If you love your cats, this is well worth the investment.  Also, the spray works great (But don't spray it around children & don't breathe the vapors.  They can really choke you up!!).