go buy one of those big yellow jacket foam broadhead targets from morells. They are only like 50 dollars and are supposedly really good. I need to take my own advice because I'm experiencing the same problems you are right now. So I stopped shooting my block directly and now I have some cheap foam targets in front of the block and now only shallow areas of the block are falling out at a time. But you're right, the target is tooooooooo expensive to just watch fall apart.
Good luck.