Suki absolutely loves playing catch/ fetch with a tennis ball but she never gives the ball back once she fetches/ catches it so the game ends so if you have anyways of stopping her from not giving back please say.
If the other two suggestions don't work try puting a long lead on your pup and lightly pulling her back with the ball in her mouth. Just like call back training this is affective especially with a treat ;)
We have a 4 month old pup, so Caden hasn't quite mastered this either, but we have to use the mini-tennis balls (it's hard for him to carry the normal size ones still, he he) and used a box cutter to make a slice and we put treats in the ball.
You show them that there are treats inside, let them smell it, and then toss,...start with short distances. In theory, that makes them bring the ball back to you and drop it, because if they don't, they don't get a treat, cause they are in the ball! But the downside is, Caden figured out that if he chews on the ball at the right angle, he can get the treats out himself.
He also fetches better inside, without distractions, like being near grass that he can munch on. Sometimes he'll chase after the ball and lose focus. He'll have that look on his face, like, what was I doing? hmmm grass.
My game of fetch w/Gibson is more like a game of fetch/tug/fetch/tug/fetch. It doesn't really bother me much, since he does bring it back to me and he has fun playing tug-o-war as well as chasing after things. So it's like 2 games in 1 haha.
after you teach the "drop" command and "leave" command...it shouldn't be too hard. Unfortunately Corgis seem to believe teasing you with the ball is more fun that you throwing and them fetching it. the proof is in the smile.