Sahara went out her doggie door once before I could get her collar on as well, but thank God she didn't go beyond her boundry. I also have the underground fence and she is afraid to go even close to the boundry. I had to spike it up b/c I found her in my neightbors yard once chasing a cat. The problem was she would not go back over the boundaries to get back in the yard. I had just got back from work when I saw her, I would freak if she disappeared. She will also chase the cars that pass my house, but stops short of the boundry. It is a good thing I have it or she would be dead by now. Sometimes when I come home from work it is dark and she is sleeping somewhere new in the house and I freak when I can't find her. I will start calling her and she comes to me slowly and stretching with a look like as if to say, " Yea, what do you want, I was sleeping sooooooo good". haha!!!!!:D