The trick is choosing the butt plug correctly. That will help prevent any injuries to the ass. Butt plugs have a tendency to want to come out of their own accord anyway, so some people will use a special belt-like device. You can get belts like this that actually will hold the butt plug in place.
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Neat video of the guy playing with his NJOY 2. I bought one of those a few years ago. It was pretty hard to get in the first time, and just when I thought it might be too big for my hole - it slid past the tight spot and popped in. It felt soooooo good! Mine weighs 1.