I wrapped black electrical tape around the plug. Worked great and didn't fall out once in 1300 miles. Very happy. Will use tape all the time. Velcro scares me.
single side 1/4 insulation tape like you see in the hardware store. unpeel the proptective cover strip on the sticky side and cut to circumference length. wrap around plug so that it seats about 1/4 inch down into the socket. works like a charm on my gps plug.