Pro tip: yes you should attack and DEFEND lava fountains. Especially today with Authority Rush running.
I keep seeing people thinking they are clever by leaving lava fountains when attacked, or putting very weak troops to defend them.
That is a mistake.
Why? Because:
You earn both CP and event points by defending the fountain. Especially if your clan turned on the 1000% CP bonus, which most clans should.
You do not lose any troops permanently, and the silver revive cost is super cheap.
The enemy clans will get their points anyway. Trying to outsmart them and prevent it is a waste of your time. They will get the needed points no matter what you do, so ignore that aspect.
Today is Authority Rush. Let that sink in for a minute. It means you can get points for new mercenaries, by attacking+defending with your mercenaries and then reviving them for cheap silver, without losing any of them!
That last point is a big deal. It's basically free mercenaries today.
I'm not even using monsters or regular troops in my lava fountain attacks - I am only using mercenaries... ALL of them. I've already gotten a bunch of new ones for essentially free.
So stop being silly. Defend your fountain, and attack the other clan's fountains.