First thing I'd check is whether or not the guts are working loose. If they are, then they'll pop out on you when you're riding.
(I saw a photo posted of a recent muffler. The construction seemed to be different than mine. So the details could be off, but the principle is the same)
First time it happened to me there was a motorcycle coming around the bend at a pretty fair distance. I thought, "Man, that bike is loud.....Wait a minute....Is that me?".
Sure enough was. Second time my rear tire ran right over the muffler guts and instantly flattened. Others have had their guts run over by cars and trucks, ruining them.
I replaced the screw that holds it together with a slightly longer, hex head bolt and lock washer. Still have to tighten occasionally, but it's not a big deal.