Copyright is complex. It can protect sound recordings, including podcasts. It protects the expression of the idea not the idea itself. So just because you said it on your podcast does not mean that you own it, but you do own the recording of you saying it.
You don’t need to register copyright and it lasts for around 70 years. Importantly, it stops other people from copying your work (though it does not stop people from doing something similar to your work).
Trademarking is different. It stops anyone using your intellectual property (including sound) or anything similar for 10 years. Essentially, it’s a monopoly right.
All of this is important when it comes to commercialising podcast. If you don’t own your content then you cannot commercialise it. And, of course, you can’t sell it.
Cliff's final thought was sobering for the audience. “Podcasters need to lawyer up” he said.