Of all the many things I've taught Piper jumping is the one thing I've had a hard time stopping. He knows the word 'off' but still pushes the limits lol, especially when his supper is on the counter! The one thing I do is when I come home (this is when he's most likely to jump) is I immediately tell him to sit as I come through the door and he listens right away. Then I take off my coat and when I'm ready I pay attention to him by getting down to his level, he loves this. You can also have a small mat and teach him to go to his mat...eventually having him go to his mat whenever someone comes to the door. Do this by standing on or near the mat and when he comes to it treat, as you perfect it add on a down when he comes to the mat (as he learns what you expect from him add the command go to your mat). You want to be close to or on the mat initially as he learns and gradually move away from it and sending him to it but just very slow progression. It's a very easy trick to teach and very helpful in many ways, can become a 'safe' place for them to be.