Our Spanish rescue dog was constantly disappearing into hedges or beyond chasing squirrels but he quickly learned to associate hedges with citronella and after just a few days he calmed down and turned his focus onto playing with balls and other dogs instead of running off. We did lose the transmitter (we think it went into a poo bin by mistake) and whilst it is not normally a replaceable item the customer services at Petsafe sourced us a replacement so 5 stars for them too!