Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Seemed to Work Great in the Beginning, but...

I've had this collar for a while now... maybe a year or so, no more than two years. I thought that it had been working okay. It was certainly stopping her from barking most of the time (she's very territorial and barks at every moving thing around). Note that I say it only stopped her most of the time. The collar didn't pick up on every bark. Recently, however, the collar has had some serious sensor malfunctions. She'll bark for a solid minute before she gets a correction (this is on a new battery). More serious, however, is that she gets a correction seemingly at random. I was concerned that in the year I've been using this collar, Bubbles never ever got the hint that barking caused the correction, and now I'm seriously worried that it's because of this random shocking.I wish I could take it back, but the best I can do right now is hope you read this and decided to spend a little more on a collar that you won't have to use forever.