A colleague and good friend here at the University of New Brunswick in Canada has used Epoxy glue to attach satellite tags to large lobsters - I can't see why Epoxy wouldn't work on a crab. If you want more information about the lobster tagging project happening here I can put you in touch with him.
We used epoxy glue to attach tags on the carapace of big portunid crabs. Don't take the superfast (5min) - it isn't that strong. We took the fast (15min) epoxy glue - worked out perfectly.