Using birds is important, as is using a bird boy that can help dog if needed. In fact I wouldn't run a long mark with this dog unless I did have a bird boy to help. And never say never, but never let s dog that has popped come back without the bird and certainly don't call them in.
One question-
Where is the dog popping? i.e. Somewhere in route, or in the area of the fall? In the area of fall is tricky.
Two recommendations.
When you are building a new marking concept...
Be sure to mix in marking tests that you know the dog can do without intervention. If every, or even a significant percentage of tests you do results in handling, the dog may start to expect it and pop. The percentage will vary between dogs.
If you have forced in back during basics (ftp), and the dog is breaking down short, a back+nick may be in order. This, should not be done in the area of the fall. Gunner help, or just reading the dog and giving a verbal back before the dog pops - don't blow the whistle, just give a BACK!
If the dog is making the area of the fall and just not persisting in the hunt, a drill like the dirt clod drill or similar may be in order.