Here are two methods to separate really stuck ferrules:
Method 1 (alone): place rod behind your knees; close knees together; grip each rod segment tightly with one hand (at the ferrule); separate knees and the rod will come apart.
Method 2 (with partner): Instead of each partner holding one segment and pulling to separate, each takes a hold of a rod segment (there will be one hand of each on each segment), and then each one pulls both hands apart at the same time. You're basically doubling the force applied in the separation process. Works well.
Applying candle wax to the male ferrule will help sections stay together when assembled, and makes it easier to pull them apart at the end of the fishing sessions.