Siouxsie Quattro sew on cloth patch

Your cities. Dust. If you know what I mean. 
and I think you do. 

Screen printed with pearlescent white ink on heavy black canvas

This style of patch has an unfinished edge. There are a couple of different methods to combat fraying.

🦇 You could hem the edge prior to attachment. Alternately you could fold the edge under and sew it on at the same time, and accomplish pretty much the same thing. (Snip the corners it will help.)

🦇you could line the underside edge with duct tape and sew through it when you attach it. (I have not tried this method)

🦇you could mod podge the edge to it (this is what I usually do)
-I’ve also heard that clear nail polish/super glue is quite effective in the same way