My dog, Katie, was fine the first week she was her (she was about 18ths old then). THen she started jumping the fence everytime I left the house. I am a stay at home mum so am home most of the time and she was quite happy to stay inside our yard when I was at home, but as soon as I left she would wait 5mins then jump the fence and away she would go. I have a tag with my mobile number on her collar and I would get phone calls from strangers saying they had her.
I borrowed an electric fence but this didnt stop her either. Had it up for about 3-4mths but she would get the zap and keep on going. So as a last resort I bought her a kennel (thanks molasseslass ) and resorted to tieing her up on a chain whenever I left the house. Didnt like doing it, but didnt want her hit by a car either!
However, the last month or so, I have not tied her up and she is happy to wait for my return.
SO, my theory (with Katie - ONLY) is that she worried I would not return and jumped to try and find me. Now that she is secure in her knowledge that I will return she is happy to wait. She knows this is home. Mind you she is a different dog now to when we got her. Much more relaxed and less timid. We are planning on moving in the next few months so will see how she goes at a new place. Will prob go back to putting her on the chain for the first few weeks just to be sure.