I've gone through about a dozen different types of stun guns. I like the stubby baton style types the most. I've found that the zappers that take at least two 9Volt batteries work great, 3 9Volt batteries even better. And yes, I took a scientific approach to testing them all. LOL. Most people will drop after a good 4-5 second burst (torso), but won't piss in their pants unless you get them with multiple zaps.
With a good stunner it is next to impossible to hold it to yourself for more than a second. But don't take my word for it, go ahead and try...