Catches that repel but do not harm?

[admiralducksauce]

I may be missing something obvious here, but what's a good way to model a catch like the ghosts on Supernatural?  If you blast them with rock salt or swing iron through them they dissipate temporarily (it seems for longer periods of time for younger or weaker spirits) but the salt/iron doesn't actually hurt them at all.

I don't see it as a Compel; after all, ghosts on the show cannot "refuse" dissipation when struck with salt or iron.  It always works.  You just can't "kill" a ghost with these methods (that Catch is salting and burning their physical remains).

[Sanctaphrax]

Maybe ghosts have no FP. I wouldn't expect positive refresh from them, you know?

Or maybe refusing the salt compel means that the salt doesn't touch you, not that you resist it.

Regardless, it sure sounds like a compel to me.

[Dravokian]

you might want to go with a form of physical immunity... instead of toughness so it doesn't cause damage and the catch causes it to dissipate for a period of time... number of exchanges = to stress... or something similar.

[EdgeOfDreams]

I'm also on the compel bandwagon here.  The GM has control of whether or not monsters and NPCs accept compels anyway.

[TheBiggs]

Well, maybe they do take stress, and the consequences are then compelled to make it disappear. The more severe the consequence, the more time it takes for them to reappear.
It's just that within the scope of the conflict, even if you take them out with salt, they won't have been killed.

[devonapple]

In Dresden, ghosts have the capacity to just go away back into their Demesne, whether they are Taken Out or not, so the salt could be (as many others have suggested) a Compel to simply go away, if the net result is only giving the heroes an exchange or two of breathing room. Anything longer than that, however, and I feel the Catch would need to have been used as a component in an attack that forced a Concession, or resulted in a Take Out.

My breakdown would be:
Ghost disappears for 1 exchange: Compel the Ghost's vulnerability
Ghost disappears for 2 exchanges: Compel + Fate Point
Ghost disappears for long enough that combat is effectively over: Ghost has Conceded the Conflict to avoid being Taken Out
Ghost gone forever (or as long as it will ever be gone): Ghost has been Taken Out

[computerking]

  If you blast them with rock salt or swing iron through them they dissipate temporarily ...   You just can't "kill" a ghost with these methods (that Catch is salting and burning their physical remains).

It looks like a Compel based on the "Repulsion" part of a Catch. Since Salting/Burning the bones is the Catch, Rock Salt shot would cause the ghost discomfort, even though it's not used in the right way.