Well..I've had the same problem and it seems to come down to buy hermits and just replenish them every few months..
The bigger hermits might last longer, but if they can get ahold of a fish, they will.
I've successfully got two emeralds in with my puffer, and he doesn't bother them (they hide in the LR
quite well), then at night they come out and help clean up.
I've also got loads of those elephant trunk snails (nassarius I think?) that go below the sand mostly during the day, and come out at night to feed.
After a couple months with the puffer, I still have the handful of small scarlet hermits I put in there..
Anything else might be at peril or a risk to the tank if the aggressors decide to get nippy (like cukes for example).
I'll keep my eye out for a solution beyond that (as I have the same prob heh)