I bought a pair of these collars because Havoc freaks out if he smells another cat outside and Toby tries to attack him and everything else within reach when this happens. Toby kept getting his stuck in his mouth so I tightened it. It eventually started rubbing his fur out so I took it off because Havoc was usually the one to start trouble. Toby kept licking it and eventually chewed it off of Havoc's neck. All of this happened within a week of putting them on the cats and Havoc still had incidents. I ended up putting a mangled one back on Havoc because he seems nervous here lately, but in the beginning they didn't solve my problems. I've stopped bringing in so much firewood from outside and spray it with some off-brand Feliway type stuff just in case and found some "calming" treats at the local Kroger, but I'm not sure if they're helping. There is no rhyme or reason as to when Havoc's gonna get upset about something.