Cat is a door darter

I brought in Tipper about 3years ago. He came to our "diner" He was very friendly obviously he had been in a home. He purred for 3 days after I brought him in!He loves to be petted and he is food obsessed. But he has darted out the door twice recently The first time I was able to snatch him up but the second time he was out for about 10 days. We could see him at the "diner" but could not get him in.He finally just walked to my husband and let my hisband carry him in. We have made a barrier which we are able to wedge between the wall and a tall folding screen. That deters him enough that we are able to get out and come in. We can see if he tries to jump and which he never has. Any other suggestions? Also I have recently brought in
a semi feral cat who is just now starting to come out of hiding
and I am afraid that she will become a door darter also. Putting them in a separate room is not an option since we are in a small condo and the only place to put the box is in the open area with the only outside door. I don't understand why he has started to want to go out after all this time

Has he been fixed? What about the new kitty? When you are leaving you could throw a favorite toy and have him go away from the door. 

thank you for your suggestion.  He has been fixed.  He ignores the new kitty for the most part (I have fostered a lot so when a new cat comes in he just thinks "how long will you be here?")  I can distract him when i leave. but then when I come back he hears the key in the door and comes running to the door.  So I guess I will just stay with the barrier for now.