Instruct: Classify the given review into positive or negative sentiment.
Query: Works well, but supervise

These collars worked well on my two eighty pound mutts who were driving my neighbors nuts. The only issue I had was when we left the collars on, unsupervised, for a day. Our dogs proceeded to chew the collars off of each other, which defeats the purpose. I will say, though, after this, the collars still worked, I just had to rig a way to put the device on our normal collars. Be sure to supervise for a little while if you have giant puppies!