I would say you need one with a tone or vibration button on it. That way you can hit that instead of zapping them. They catch on pretty quick. But I do not agree with at all hitting the button everytime the dog gets past 40 yards. You will discourage him from hunting. The dog will slowly lose desire to hunt, and think that its job is to just stay close to the master no matter what, even if it smells a bird 10 yards beyond its limit. Does the dog not point? Arent they a pointing dog? I think the reinforcement of "whoa" and not creeping on point is what you are looking for here. If they point a bird too far out and flush it because they are to close to it, they will gradually learn to keep their distance. Or at that point you can hit the tone button to stop them. Assuming you teach them to stop with tone. Example: My little setter does flush pheasants sometimes because she gets too close and she's too far out for me to shoot. It gets up, she gives chase, I immediately hit the vibrate button to keep her from chasing it. Then when I get to her I release her again. Then usually the next time she holds from a distance where I can get the bird. Then she may go bump another one and I repeat the process. But having the dog shocked like you have a constant invisible fence around you in a 40 yard circle is asking quite a bit from an animal and I don't think it will be beneficial to your dog or you finding more birds.