both spellings are acceptable. the definition of "curb" as a verb is also consistent with its function as a noun. the difference is cultural, since "kerb" is only the preferred spelling in some places outside of english-speaking areas of North America.

"the city installed a kerb on the roadway to curb dangerous incidents of motor vehicle and pedestrian traffic"

"spelt" follows the same geographical distinction, as "spelled" is the preferred spelling for American english.

still, "kerby" is clearly the better pun, so thank you for that.

Actually, it's spelled curb in the US