apologies if this would be better in the rules & mechanics forum.

My crew are about to face a variation on the Path of Blades (in a home brew). It's written as requiring a DC15 Int (Arcana) check to get past the rune at the end but, and I may just be being dumb here, what are they actually supposed to be doing here and how would they know they are doing it? It just feels like they need to be doing something like, i don't know, tracing a symbol in the air or something. Have any of you used this trap and how did you handle this part of it?

Also, when they get past the rune of fear do you have that deactivate the whole trap or does everyone still have to get through the other bits of it (I may just play this by ear according to how effed up they all are).

Any thoughts appreciated. 

"Path" obviously

I'm going by the version in the UA article, in case you're looking at a different version.

It's not usual to call for Arcana checks to disable a magical effect. PCs trained in magic/arcana should be informed that they can generally do this kind of thing in situations such as these. It's kind of intentionally left vague so that different classes might describe their check in different ways, but essentially they are disrupting the magic somehow. Maybe an artificer sends out an automaton to scratch off a particular rune on the wall. Maybe a cleric emits divine energy in a particular pattern that works to nullify the enchantment. Maybe the abjuration wizard sets up a ward around the source of the magic. My players generally handle this themselves, but you can make suggestions if they aren't used to using the skill like this.

Personally I think the alternative method requiring three castings of dispel magic is way overboard in this design. One dispel magic is worth roughly three successful arcana checks IMO, but I suppose it depends on how often you are letting the party long rest.

Since the trap is broken into three parts and each part has different countermeasures, I don't think that disabling the rune is meant to disable the whole thing. Although you might rule that disabling two parts could deactivate the whole thing (I might do this if it starts feeling tedious or the party is getting frustrated/rolling really poorly).

thank you, that's really helpful. We'll see how effed up they are once they're through to see if they need to do it all over again to get back out. Perhaps I'll add some kind of mechanism they can find in the room after which will disable the whole thing.