Help! Wanting to free my Oreodont fossil skull from its rock!

For context: I bought this Oreodont skull from ebay a long time ago. Its skull is about 60% shown as the rest is embedded into the rock still. Anyways, it look like the rock can be broken off more but I don’t want to accidentally break off huge chunks of the fossil.

What are safe ways to “peel back” the rock as to not destroy the skull in the process?