Keep your slip lead short, or a collar hold and, without causing discomfort, gently move the head toward the beam as it 'sweeps' the field. Until the penny drops.
Try not to lamp aeroplanes when first entering a field, keep your beam low!!
Forget about squatters, no matter how 'obvious' they may seem!
Direct your dog to 'moving' targets only, directing that head gently...
Let your dog 'tune in' to stuff in the beam and up and moving without a chance of a slip. Let it see moving targets, without the chance of missing, it'll 'gee' it up (don't over egg this!) and realise that the game is clo