i know a lot of people already use spray insulation foam to fix there 3d targets. just spray it in and let it fill the hole. i found out a better way last night though. instead of filling the hole and letting the foam bubble out i turned the target and laid it flat agains concrete. this way all the foam stayed inside of the hole and was much denser then if you would have just let it bubble out.
however i didn't do this to the other side, i just let it bubble out. what do you guys use to scrape off the extra foam.
a sharp macheté
Here is a better way to patch than laying the side on concrete.
http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=048562
I've used Eric's method and it works well. No offense Eric.......but I have found something to take your method to the next level.
Shrink Wrap. You can wrap the target really tight with 3 or 4 wraps and then just slice it with a razor knife and peels right off.