I've never had trouble with Shake, but I may have just been lucky. What I usually do, is offer my hand palm up and when he looks at it I say shake. I just expect a blank stare at that point, but before he stops looking at the hand reach and grab his paw. Deliberate but not rushed. Treat while holding the paw.
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Apsel der Schwarzbar -- Dark Sable -- 10/31/2013