I would reccommend a bottle of lock-tite, and a wrench small enough for the nut on the back of your muffler.

Check your muffler during pre-flight, and post-flight every flight.

If the exhaust port is ever in a different position upon landing, immediately take off the nut, re-locktite, and put it back on.

This will save you from purchasing a new muffler.

I lost the back of my muffler during loops, all of a sudden the engine died while I was vertical. First unexpected dead stick. Best landing of the day, but I wasted $15 and 1 hour getting my plane to fly again.