I used to use a Silent Dog whistle to make them come out and stick their heads up. I wore it around my neck, when one ducked, I'd blow the whistle.
Often times, 3 or 4 in a den would come out. Watch carefully which way they are looking, shoot the furtherest one away from the way they are all looking. Try to take off just the top of the head, and often you may just kill them all. Keep blowing the whistle as you are shooting to keep their attention focused on you instead of the one that is flopp'en. If one looks at the one flopp'en, shoot him next.