Tubby used to do the same thing when he was younger. First of all, everyone in the house has to be aware that he is doing this, and they have to be on guard every time they open the door. The one time they let their guard down he will be ready and will dash out again.

What worked for Tubby I wouldn't recommend (door slamming on his tail - ouch!) but what I would recommend is that whenever anybody wants to go out and he is waiting to dash, he must be told NO in a very firm tone, and I point my finger at him - don't know if that helps or not. The first few times he will still try and dash out. Be prepared and catch him or somehow stop him. Pick him up and put him away from the door and tell him again NO. It will take some patience, but eventually he will get the idea. Also, make sure that whenever somebody comes in the door they are prepared to stop him. If I have packages, I normally let the bags hang down low so even though the door is open, Tubby's path is blocked by the bags. That gives me enough time to affirm the NO and he gets the hint and backs off.

Tubby is now 17 and still dashes on occassion. It's been at least 2 or 3 years since he's been successful, and that time was only because Terry (bf) hadn't been trained properly. Now I can tell Tubby NO and I can open the door and come and go as I please and he will not attempt to run out. It's only when I open the door and so "OK Tubby, come on out." that he runs out. And then he runs out like he's dashing, and like he's saying to himself "Oh boy! I get to go out! Oh boy!" It's like he thinks he's getting away with something.

Like I say, this will take patience, and everyone in the house needs to do this, but eventually it should work. Good luck and hopefully others will have some more suggestions.