Gaffers' tape.
Hi Steve,
In the cheerful and never ending struggle with our common language I observe that, in American English at least, that type of compound noun (a collective with a possessive serving as an adjective to restrict the noun) uses a singular possessive: gaffer's tape, sheppard's pie, etc. Apparently it is the tape of a single, representative gaffer, not all gaffers. Doesn't really make any sense, to me at least, but little in language does. I bring it up because I know you care.
As for Geoff's gaffe tape, that's excellent. That's what I'm calling it from now on.
Best,
--Frank