i have a lab that is like a david copperfeild of dogs i cannot keep him in any pen he even escapes from the house by turning the deadbolt so i was leary but went ahead and tried the pet safe wireless fence. its been 2.5 years and great i do have to stay on top of the batteries cause he will try it out every few months and if its dead he's gone but if not he stays the batt usually last 2 monthe so about 3 bucks every two months aint bad. what happens with a fence with the wire is that it knows no sides so if he runs through it it'll stop shocking the wireless is a radio feild so when he crosses is continues to shock till he returns or the batt dies.