Okay well I'm not a pro or anything but your probelm could be that you've sort of taught them that if they don't come you'll go out and get them. In other words they aren't playing deaf they're giving you the doggie dew claw knowing very well that you'll eventually come out and get them.

Here's what I would do if I were in your position, if I let them out and then called them and they didn't come right away when called I would leave them out there until they knew that you were playing their came anymore. Also if you use a recall word and they don't come when that word is used and you have to go and get them you've showed them that word has no meaning so you might want to switch the recall word and ONLY use it when you know that they will come.

Another thing to try and this is going to sound really dumb but it works honest it does, we use it all the time in agility, is to call the dog and then rather then approach them and keep calling them, call them and then turn and run. Most dogs will give chase because it's their nature so to speak. Think of it as a game, you call them, run and if they chase you and catch you they get praise and or treats.

That's all I can think of, but like I said I'm not a pro.