If the deer isn't alert, they aren't likely to jump the string. Like davidmil, if I think the deer is going to come closer, I'll wait. If not, I'll take the shot applying the appropriate lead -- also like davidmil, I don't grunt deer to a stop.

If the deer is alert and suspicious, I'll purposely aim at the bottom of the kill zone. If it doesn't drop, I've still got 'em. On the deer that I've taken where this happened, the deer have dropped into a perfect kill shots.

I practice out to 60+ yards. I did so just yesterday and was getting pretty tight groups out to 60. I limit myself on real deer to 40 yards taking one last year at that range. It was in a field and walking. After I shot, it went about 50 yards and fell over without even kicking.