Hermits and urchins: incompatible?

[pseudorand]

I just got half a dozen very small hermit crabs. Along with a bunch of empty shells. Shells keep ending up on my urchins as is wants to happen. it's nearly impossible to tell if the shell has a hermit in it. So I end up picking it off the urchin. This is getting annoying.

Does anyone have a solution to this problem? Are hermits smart enough to stay away from urchins? Can I assume if it's stuck to an urchin it's probably not a crab?

 

[Mr_Knightley]

I have had similar things happen to me, it's never an issue as my urchins always drop the crab within an hour or two. You could potentially give the urchin something that covers it's whole top half (Black suction cups work best) to keep the urchin occupied. It would use the cup instead of the crabs and the issue, theoretically, would no longer be.