That's some mean squirrels! I use the clamshells for guava and so far it's worked 100%. I still lose most that aren't protected. For smaller clamshells, I've seen them nibbling on parts that come in contact with any holes in the clamshells. Not too bad for guavas that can callous over. I don't yet have mangos to test it on them. I did try them on avocados before, for rats instead, but I found they would chew the stem, or just knock them off with their weight presumably, so the avocado would fall down, and then sometimes make it through the packaging. At least with guava, the clamshell is wrapped around the whole branch so it's secured pretty well.