when you lamp off the back of the van your dog has to be able to jump,mostly its gates and wire,but sometimes if you need to stop at a certain part of the field where there is no gap the dog needs to be able to jump the hedge,but its up to the individual to decide wheather its safe(know the field) for the dog to do so. i have only see a hand full of dogs that will jump a hedge regularly,and i mean one it cant see over.i think dogs do it with experience,they get to know(in my style of lamping) when the van stops theres something over the other side,some if they want it bad enough will jump over