I have a gyp that has never bayed a hog in a pen and she's 5 years old. She'll sure enough get out and find/bay them in the woods though. I put more stock in what they'll do in the woods compared to what they'll do in a pen. Bayin' is not so hard...it's the findin' that's a little tricky

Then again, I usually start mine early going to the woods.
Try draggin a small hog into the woods and tying it off and see if the pups will find it.